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A cactus (, or less commonly, cactus) is a member of the plant family Cactaceae, a family comprising about 127 genera with some 1750 known species of the order
Caryophyllales Caryophyllales ( ) is a diverse and heterogeneous order of flowering plants that includes the cacti, carnations, amaranths, ice plants, beets, and many carnivorous plants. Many members are succulent, having fleshy stems or leaves. The betala ...
. The word ''cactus'' derives, through Latin, from the Ancient Greek word (''káktos''), a name originally used by Theophrastus for a spiny plant whose identity is now not certain. Cacti occur in a wide range of shapes and sizes. Although some species live in quite humid environments, most cacti live in habitats subject to at least some drought. Many live in extremely dry environments, even being found in the
Atacama Desert The Atacama Desert ( es, Desierto de Atacama) is a desert plateau in South America covering a 1,600 km (990 mi) strip of land on the Pacific coast, west of the Andes Mountains. The Atacama Desert is the driest nonpolar desert in the w ...
, one of the driest places on Earth. Because of this, cacti show many adaptations to conserve water. For example, almost all cacti are succulents, meaning they have thickened, fleshy parts adapted to store water. Unlike many other succulents, the stem is the only part of most cacti where this vital process takes place. Most species of cacti have lost true leaves, retaining only spines, which are highly modified leaves. As well as defending against
herbivore A herbivore is an animal anatomically and physiologically adapted to eating plant material, for example foliage or marine algae, for the main component of its diet. As a result of their plant diet, herbivorous animals typically have mouthp ...
s, spines help prevent water loss by reducing air flow close to the cactus and providing some shade. In the absence of true leaves, cacti's enlarged stems carry out photosynthesis. Cacti are native to the Americas, ranging from Patagonia in the south to parts of western Canada in the north—except for ''
Rhipsalis baccifera ''Rhipsalis baccifera'', commonly known as the mistletoe cactus, is an epiphytic cactus which originates from Central and South America, the Caribbean, and Florida. It is also found throughout the tropics of Africa and into Sri Lanka where it ...
'', which also grows in
Africa Africa is the world's second-largest and second-most populous continent, after Asia in both cases. At about 30.3 million km2 (11.7 million square miles) including adjacent islands, it covers 6% of Earth's total surface area ...
and Sri Lanka. Cactus spines are produced from specialized structures called
areole In botany, areoles are small light- to dark-colored bumps on cacti out of which grow clusters of spines. Areoles are important diagnostic features of cacti, and identify them as a family distinct from other succulent plants. Gordon Rowley - ...
s, a kind of highly reduced branch. Areoles are an identifying feature of cacti. As well as spines, areoles give rise to flowers, which are usually tubular and multipetaled. Many cacti have short growing seasons and long dormancies and are able to react quickly to any rainfall, helped by an extensive but relatively shallow root system that quickly absorbs any water reaching the ground surface. Cactus stems are often ribbed or fluted, which allows them to expand and contract easily for quick water absorption after rain, followed by retention over long drought periods. Like other succulent plants, most cacti employ a special mechanism called "
crassulacean acid metabolism Crassulacean acid metabolism, also known as CAM photosynthesis, is a carbon fixation pathway that evolved in some plants as an adaptation to arid conditions that allows a plant to photosynthesize during the day, but only exchange gases at night. I ...
" (CAM) as part of photosynthesis. Transpiration, during which carbon dioxide enters the plant and water escapes, does not take place during the day at the same time as photosynthesis, but instead occurs at night. The plant stores the carbon dioxide it takes in as malic acid, retaining it until daylight returns, and only then using it in photosynthesis. Because transpiration takes place during the cooler, more humid night hours, water loss is significantly reduced. Many smaller cacti have globe-shaped stems, combining the highest possible volume for water storage with the lowest possible surface area for water loss from transpiration. The tallest free-standing cactus is '' Pachycereus pringlei'', with a maximum recorded height of , and the smallest is '' Blossfeldia liliputiana'', only about in diameter at maturity. A fully grown saguaro (''
Carnegiea gigantea The saguaro (, ) (''Carnegiea gigantea'') is a tree-like cactus species in the monotypic genus ''Carnegiea'' that can grow to be over tall. It is native to the Sonoran Desert in Arizona, the Mexican state of Sonora, and the Whipple Mountains ...
'') is said to be able to absorb as much as of water during a rainstorm. A few species differ significantly in appearance from most of the family. At least superficially, plants of the genera ''
Leuenbergeria ''Leuenbergeria '' is a genus of flowering plant in the family Cactaceae, mostly native around the Caribbean. Unlike most cacti, it has persistent leaves and develops bark on its stems early in its growth. The genus was created in 2012 by Joël L ...
'', ''
Rhodocactus ''Rhodocactus'' is a genus of flowering plant in the cactus family Cactaceae, native to central South America. Unlike most species of cacti, ''Rhodocactus'' has persistent leaves and a fully tree-like habit. The genus was sunk into a broadly ...
'' and ''
Pereskia ''Pereskia'' is a small genus of about four species of cacti that do not look much like other types of cacti, having substantial leaves and non-succulent stems. The genus is named after Nicolas-Claude Fabri de Peiresc, a 16th-century French bota ...
'' resemble other trees and shrubs growing around them. They have persistent leaves, and when older, bark-covered stems. Their areoles identify them as cacti, and in spite of their appearance, they, too, have many adaptations for water conservation. ''Leuenbergeria'' is considered close to the ancestral species from which all cacti evolved. In tropical regions, other cacti grow as forest climbers and
epiphyte An epiphyte is an organism that grows on the surface of a plant and derives its moisture and nutrients from the air, rain, water (in marine environments) or from debris accumulating around it. The plants on which epiphytes grow are called phoroph ...
s (plants that grow on trees). Their stems are typically flattened, almost leaf-like in appearance, with fewer or even no spines, such as the well-known Christmas cactus or Thanksgiving cactus (in the genus ''
Schlumbergera ''Schlumbergera'' is a small genus of cacti with six to nine species found in the coastal mountains of south-eastern Brazil. These plants grow on trees or rocks in habitats that are generally shady with high humidity, and can be quite differen ...
''). Cacti have a variety of uses: many species are used as ornamental plants, others are grown for fodder or forage, and others for food (particularly their fruit).
Cochineal The cochineal ( , ; ''Dactylopius coccus'') is a scale insect in the suborder Sternorrhyncha, from which the natural dye carmine is derived. A primarily sessile parasite native to tropical and subtropical South America through North America ...
is the product of an insect that lives on some cacti. Many succulent plants in both the
Old Old or OLD may refer to: Places *Old, Baranya, Hungary *Old, Northamptonshire, England * Old Street station, a railway and tube station in London (station code OLD) *OLD, IATA code for Old Town Municipal Airport and Seaplane Base, Old Town, M ...
and New World – such as some Euphorbiaceae (euphorbias) – are also spiny stem succulents and because of this are sometimes incorrectly referred to as "cactus".


Morphology

The 1,500 to 1,800 species of cacti mostly fall into one of two groups of "core cacti": opuntias (subfamily
Opuntioideae Opuntioideae is a subfamily of the cactus family, Cactaceae. It contains 15 genera divided into five tribes. The subfamily encompasses roughly 220–250 species, and is geographically distributed throughout the New World from Canada, to Argentina ...
) and "cactoids" (subfamily
Cactoideae The Cactoideae are the largest subfamily of the cactus family, Cactaceae. Around 80% of cactus species belong to this subfamily. , the internal classification of the family Cactaceae remained uncertain and subject to change. A classification inc ...
). Most members of these two groups are easily recognizable as cacti. They have fleshy succulent stems that are major
organs In biology, an organ is a collection of tissues joined in a structural unit to serve a common function. In the hierarchy of life, an organ lies between tissue and an organ system. Tissues are formed from same type cells to act together in a ...
of photosynthesis. They have absent, small, or transient
leaves A leaf ( : leaves) is any of the principal appendages of a vascular plant stem, usually borne laterally aboveground and specialized for photosynthesis. Leaves are collectively called foliage, as in "autumn foliage", while the leaves, ste ...
. They have
flowers A flower, sometimes known as a bloom or blossom, is the reproductive structure found in flowering plants (plants of the division Angiospermae). The biological function of a flower is to facilitate reproduction, usually by providing a mechanism ...
with
ovaries The ovary is an organ in the female reproductive system that produces an ovum. When released, this travels down the fallopian tube into the uterus, where it may become fertilized by a sperm. There is an ovary () found on each side of the body. T ...
that lie below the sepals and
petals Petals are modified leaves that surround the reproductive parts of flowers. They are often brightly colored or unusually shaped to attract pollinators. All of the petals of a flower are collectively known as the ''corolla''. Petals are usually ...
, often deeply sunken into a fleshy receptacle (the part of the stem from which the flower parts grow). All cacti have
areole In botany, areoles are small light- to dark-colored bumps on cacti out of which grow clusters of spines. Areoles are important diagnostic features of cacti, and identify them as a family distinct from other succulent plants. Gordon Rowley - ...
s—highly specialized short
shoots In botany, a plant shoot consists of any plant stem together with its appendages, leaves and lateral buds, flowering stems, and flower buds. The new growth from seed germination that grows upward is a shoot where leaves will develop. In the spr ...
with extremely short
internodes A stem is one of two main structural axes of a vascular plant, the other being the root. It supports leaves, flowers and fruits, transports water and dissolved substances between the roots and the shoots in the xylem and phloem, stores nutrien ...
that produce spines, normal shoots, and flowers. The remaining cacti fall into only two groups: three tree-like genera, ''
Leuenbergeria ''Leuenbergeria '' is a genus of flowering plant in the family Cactaceae, mostly native around the Caribbean. Unlike most cacti, it has persistent leaves and develops bark on its stems early in its growth. The genus was created in 2012 by Joël L ...
'', ''
Pereskia ''Pereskia'' is a small genus of about four species of cacti that do not look much like other types of cacti, having substantial leaves and non-succulent stems. The genus is named after Nicolas-Claude Fabri de Peiresc, a 16th-century French bota ...
'' and ''
Rhodocactus ''Rhodocactus'' is a genus of flowering plant in the cactus family Cactaceae, native to central South America. Unlike most species of cacti, ''Rhodocactus'' has persistent leaves and a fully tree-like habit. The genus was sunk into a broadly ...
'' (all formerly placed in ''Pereskia''), and the much smaller ''
Maihuenia ''Maihuenia'' is a genus of cactus (family Cactaceae) and the sole genus of the subfamily Maihuenioideae, which is the smallest subfamily of the Cactaceae. The genus comprises two cushion-forming, mucilaginous species. They are found at high elev ...
''. These two groups are rather different from other cacti, which means any description of cacti as a whole must frequently make exceptions for them. Species of the first three genera superficially resemble other tropical forest trees. When mature, they have woody stems that may be covered with
bark Bark may refer to: * Bark (botany), an outer layer of a woody plant such as a tree or stick * Bark (sound), a vocalization of some animals (which is commonly the dog) Places * Bark, Germany * Bark, Warmian-Masurian Voivodeship, Poland Arts, e ...
and long-lasting leaves that provide the main means of photosynthesis. Their flowers may have superior ovaries (i.e., above the points of attachment of the sepals and petals) and areoles that produce further leaves. The two species of ''Maihuenia'' have succulent but non-photosynthetic stems and prominent succulent leaves.


Growth habit

Cacti show a wide variety of growth
habits A habit (or wont as a humorous and formal term) is a routine of behavior that is repeated regularly and tends to occur subconsciously.
, which are difficult to divide into clear, simple categories. ; Cacti can be tree-like (arborescent), meaning they typically have a single more-or-less woody
trunk Trunk may refer to: Biology * Trunk (anatomy), synonym for torso * Trunk (botany), a tree's central superstructure * Trunk of corpus callosum, in neuroanatomy * Elephant trunk, the proboscis of an elephant Computing * Trunk (software), in rev ...
topped by several to many
branch A branch, sometimes called a ramus in botany, is a woody structural member connected to the central trunk of a tree (or sometimes a shrub). Large branches are known as boughs and small branches are known as twigs. The term ''twig'' usually ...
es. In the genera ''Leuenbergeria'', ''Pereskia'' and ''Rhodocactus'', the branches are covered with leaves, so the species of these genera may not be recognized as cacti. In most other cacti, the branches are more typically cactus-like, bare of leaves and bark and covered with spines, as in '' Pachycereus pringlei'' or the larger opuntias. Some cacti may become tree-sized but without branches, such as larger specimens of ''
Echinocactus platyacanthus ''Echinocactus platyacanthus'', also known as the giant barrel cactus, golden barrel cactus, giant viznaga, or biznaga de dulce, is a species of cactus (family Cactaceae). It is native to central Mexico in the Chihuahuan Desert. This species is t ...
''. Cacti may also be described as shrubby, with several stems coming from the ground or from branches very low down, such as in '' Stenocereus thurberi''. ; Smaller cacti may be described as columnar. They consist of erect, cylinder-shaped stems, which may or may not branch, without a very clear division into trunk and branches. The boundary between columnar forms and tree-like or shrubby forms is difficult to define. Smaller and younger specimens of ''
Cephalocereus senilis ''Cephalocereus senilis'', the old man cactus, is a species of cactus native to Hidalgo and Veracruz in central Mexico. It is threatened in the wild, but widespread propagation and popularity in cultivation have reduced the demand on wild popula ...
'', for example, are columnar, whereas older and larger specimens may become tree-like. In some cases, the "columns" may be horizontal rather than vertical. Thus, '' Stenocereus eruca'' can be described as columnar even though it has stems growing along the ground, rooting at intervals. ; Cacti whose stems are even smaller may be described as globular (or globose). They consist of shorter, more ball-shaped stems than columnar cacti. Globular cacti may be solitary, such as '' Ferocactus latispinus'', or their stems may form clusters that can create large mounds. All or some stems in a cluster may share a common root. ; Other forms Other cacti have a quite different appearance. In tropical regions, some grow as forest climbers and
epiphyte An epiphyte is an organism that grows on the surface of a plant and derives its moisture and nutrients from the air, rain, water (in marine environments) or from debris accumulating around it. The plants on which epiphytes grow are called phoroph ...
s. Their stems are typically flattened and almost leaf-like in appearance, with few or even no spines. Climbing cacti can be very large; a specimen of ''
Hylocereus ''Hylocereus'' is a former genus of epiphytic cacti, often referred to as night-blooming cactus (though the term is also used for many other cacti). Several species previously placed in the genus have large edible fruits, which are known as pitay ...
'' was reported as long from root to the most distant stem. Epiphytic cacti, such as species of ''
Rhipsalis ''Rhipsalis'' is a genus of epiphytic flowering plants in the cactus family, typically known as mistletoe cacti. They are found in parts of Central America, the Caribbean and northern regions of South America. They also inhabit isolated location ...
'' or ''
Schlumbergera ''Schlumbergera'' is a small genus of cacti with six to nine species found in the coastal mountains of south-eastern Brazil. These plants grow on trees or rocks in habitats that are generally shady with high humidity, and can be quite differen ...
'', often hang downwards, forming dense clumps where they grow in trees high above the ground. Pereskia aculeata5.jpg, Treelike habit (''
Pereskia aculeata ''Pereskia aculeata'' is a scrambling shrub in the family Cactaceae. Common names include Barbados gooseberry, blade-apple cactus, leaf cactus, rose cactus, and lemonvine. It is native to tropical America. The leaves and fruits are edible, conta ...
'') Cardon Pachycereus pringlei.jpg, Tall treelike habit ('' Pachycereus pringlei'') Cephalocereus columna-trajani rev.jpg, Tall unbranched columnar habit (''
Cephalocereus ''Cephalocereus'' is a genus of slow-growing, columnar-shaped, blue-green cacti. The genus is native to Mexico. Description These cacti show a columnar and upright growth habit, and may be branched or unbranched reaching heights of 10 to 12 met ...
'') Ferocactus1.jpg, Shorter clustered columnar habit (''
Ferocactus pilosus ''Ferocactus pilosus'', also known as Mexican lime cactus (''Biznaga De Lima'') or Mexican fire barrel, is a species of cactus in North America. Distribution The cactus is endemic to the Chihuahuan Desert, located in northeastern Mexico., p. ...
'') Ferocactus echidne var victoriensis 1.jpg, Solitary globular habit ('' Ferocactus echidne'') Rebutia flavistylus 2 rev.jpg, Clustered globular habit (''
Rebutia ''Rebutia'' is a genus of flowering plants in the family Cactaceae, native to Bolivia and Argentina. They are generally small, colorful cacti, globular in form, which freely produce flowers that are relatively large in relation to the body. They ...
'' species) Rhipsalis paradoxa.jpg, Epiphytic cactus ('' Rhipsalis paradoxa'')


Stems

The leafless, spiny stem is the characteristic feature of the majority of cacti (and all of those belonging to the largest subfamily, the
Cactoideae The Cactoideae are the largest subfamily of the cactus family, Cactaceae. Around 80% of cactus species belong to this subfamily. , the internal classification of the family Cactaceae remained uncertain and subject to change. A classification inc ...
). The stem is typically succulent, meaning it is adapted to store water. The surface of the stem may be smooth (as in some species of '' Opuntia'') or covered with protuberances of various kinds, which are usually called tubercles. These vary from small "bumps" to prominent, nipple-like shapes in the genus ''
Mammillaria ''Mammillaria'' is one of the largest genera in the cactus family (Cactaceae), with currently 200 known species and varieties recognized. Most of the mammillaria are native to Mexico, but some come from the southwest United States, the Caribb ...
'' and outgrowths almost like leaves in ''
Ariocarpus ''Ariocarpus'' is a small genus of succulent, subtropical plants of the family Cactaceae. The name comes from the ancient Greek "aria" (an oak type) and "carpos" (=fruit) because of the resemblance of the fruit of the two genus in acorn for ...
'' species. The stem may also be ribbed or fluted in shape. The prominence of these ribs depends on how much water the stem is storing: when full (up to 90% of the mass of a cactus may be water), the ribs may be almost invisible on the swollen stem, whereas when the cactus is short of water and the stems shrink, the ribs may be very visible. The stems of most cacti are some shade of green, often bluish or brownish green. Such stems contain
chlorophyll Chlorophyll (also chlorophyl) is any of several related green pigments found in cyanobacteria and in the chloroplasts of algae and plants. Its name is derived from the Greek words , ("pale green") and , ("leaf"). Chlorophyll allow plants to ...
and are able to carry out photosynthesis; they also have stomata (small structures that can open and close to allow passage of gases). Cactus stems are often visibly waxy.


Areoles

Areole In botany, areoles are small light- to dark-colored bumps on cacti out of which grow clusters of spines. Areoles are important diagnostic features of cacti, and identify them as a family distinct from other succulent plants. Gordon Rowley - ...
s are structures unique to cacti. Although variable, they typically appear as woolly or hairy areas on the stems from which spines emerge. Flowers are also produced from areoles. In the genus ''
Leuenbergeria ''Leuenbergeria '' is a genus of flowering plant in the family Cactaceae, mostly native around the Caribbean. Unlike most cacti, it has persistent leaves and develops bark on its stems early in its growth. The genus was created in 2012 by Joël L ...
'', believed similar to the ancestor of all cacti, the areoles occur in the axils of leaves (i.e. in the angle between the leaf stalk and the stem). In leafless cacti, areoles are often borne on raised areas on the stem where leaf bases would have been. Areoles are highly specialized and very condensed shoots or branches. In a normal shoot, nodes bearing leaves or flowers would be separated by lengths of stem (internodes). In an areole, the nodes are so close together, they form a single structure. The areole may be circular, elongated into an oval shape, or even separated into two parts; the two parts may be visibly connected in some way (e.g. by a groove in the stem) or appear entirely separate (a dimorphic areole). The part nearer the top of the stem then produces flowers, the other part spines. Areoles often have multicellular hairs ( trichomes) that give the areole a hairy or woolly appearance, sometimes of a distinct color such as yellow or brown. In most cacti, the areoles produce new spines or flowers only for a few years and then become inactive. This results in a relatively fixed number of spines, with flowers being produced only from the ends of stems, which are still growing and forming new areoles. In ''Pereskia'', a genus close to the ancestor of cacti, areoles remain active for much longer; this is also the case in '' Opuntia'' and ''
Neoraimondia ''Neoraimondia'' is a genus of medium to large cacti from Peru. The genus is named after the Italian-born Peruvian explorer, naturalist, and scientist, Antonio Raimondi. It is a psychoactive cacti and its different cacti have been known to ...
''.


Leaves

The great majority of cacti have no visible
leaves A leaf ( : leaves) is any of the principal appendages of a vascular plant stem, usually borne laterally aboveground and specialized for photosynthesis. Leaves are collectively called foliage, as in "autumn foliage", while the leaves, ste ...
; photosynthesis takes place in the stems (which may be flattened and leaflike in some species). Exceptions occur in three (taxonomically, four) groups of cacti. All the species of ''
Leuenbergeria ''Leuenbergeria '' is a genus of flowering plant in the family Cactaceae, mostly native around the Caribbean. Unlike most cacti, it has persistent leaves and develops bark on its stems early in its growth. The genus was created in 2012 by Joël L ...
'', ''
Pereskia ''Pereskia'' is a small genus of about four species of cacti that do not look much like other types of cacti, having substantial leaves and non-succulent stems. The genus is named after Nicolas-Claude Fabri de Peiresc, a 16th-century French bota ...
'' and ''
Rhodocactus ''Rhodocactus'' is a genus of flowering plant in the cactus family Cactaceae, native to central South America. Unlike most species of cacti, ''Rhodocactus'' has persistent leaves and a fully tree-like habit. The genus was sunk into a broadly ...
'' are superficially like normal trees or shrubs and have numerous leaves with a midrib and a flattened blade (lamina) on either side. This group is paraphyletic, forming two taxonomic
clades A clade (), also known as a monophyletic group or natural group, is a group of organisms that are monophyletic – that is, composed of a common ancestor and all its lineal descendants – on a phylogenetic tree. Rather than the English term, t ...
. Many cacti in the opuntia group (subfamily
Opuntioideae Opuntioideae is a subfamily of the cactus family, Cactaceae. It contains 15 genera divided into five tribes. The subfamily encompasses roughly 220–250 species, and is geographically distributed throughout the New World from Canada, to Argentina ...
) also have visible leaves, which may be long-lasting (as in ''
Pereskiopsis ''Pereskiopsis'' is a genus of cactus (family Cactaceae) in the subfamily Opuntioideae. Unlike typical cacti, it has persistent fleshy leaves. The genus name refers to its resemblance to the genus '' Pereskia''. Most species are found in Mexico ...
'' species) or produced only during the growing season and then lost (as in many species of '' Opuntia''). The small genus ''
Maihuenia ''Maihuenia'' is a genus of cactus (family Cactaceae) and the sole genus of the subfamily Maihuenioideae, which is the smallest subfamily of the Cactaceae. The genus comprises two cushion-forming, mucilaginous species. They are found at high elev ...
'' also relies on leaves for photosynthesis. The structure of the leaves varies somewhat between these groups. Opuntioids and ''Maihuenia'' have leaves that appear to consist only of a midrib. Even those cacti without visible photosynthetic leaves do usually have very small leaves, less than long in about half of the species studied and almost always less than long. The function of such leaves cannot be photosynthesis; a role in the production of plant hormones, such as
auxin Auxins (plural of auxin ) are a class of plant hormones (or plant-growth regulators) with some morphogen-like characteristics. Auxins play a cardinal role in coordination of many growth and behavioral processes in plant life cycles and are essenti ...
, and in defining
axillary bud The axillary bud (or lateral bud) is an embryonic or organogenic shoot located in the axil of a leaf. Each bud has the potential to form shoots, and may be specialized in producing either vegetative shoots (stems and branches) or reproductive sh ...
s has been suggested.


Spines

Botanically, " spines" are distinguished from "thorns": spines are modified leaves, and thorns are modified branches. Cacti produce spines, always from areoles as noted above. Spines are present even in those cacti with leaves, such as ''
Pereskia ''Pereskia'' is a small genus of about four species of cacti that do not look much like other types of cacti, having substantial leaves and non-succulent stems. The genus is named after Nicolas-Claude Fabri de Peiresc, a 16th-century French bota ...
'', ''
Pereskiopsis ''Pereskiopsis'' is a genus of cactus (family Cactaceae) in the subfamily Opuntioideae. Unlike typical cacti, it has persistent fleshy leaves. The genus name refers to its resemblance to the genus '' Pereskia''. Most species are found in Mexico ...
'' and ''
Maihuenia ''Maihuenia'' is a genus of cactus (family Cactaceae) and the sole genus of the subfamily Maihuenioideae, which is the smallest subfamily of the Cactaceae. The genus comprises two cushion-forming, mucilaginous species. They are found at high elev ...
'', so they clearly evolved before complete leaflessness. Some cacti only have spines when young, possibly only when seedlings. This is particularly true of tree-living cacti, such as ''
Rhipsalis ''Rhipsalis'' is a genus of epiphytic flowering plants in the cactus family, typically known as mistletoe cacti. They are found in parts of Central America, the Caribbean and northern regions of South America. They also inhabit isolated location ...
'' and ''
Schlumbergera ''Schlumbergera'' is a small genus of cacti with six to nine species found in the coastal mountains of south-eastern Brazil. These plants grow on trees or rocks in habitats that are generally shady with high humidity, and can be quite differen ...
'', but also of some ground-living cacti, such as ''
Ariocarpus ''Ariocarpus'' is a small genus of succulent, subtropical plants of the family Cactaceae. The name comes from the ancient Greek "aria" (an oak type) and "carpos" (=fruit) because of the resemblance of the fruit of the two genus in acorn for ...
''. The spines of cacti are often useful in identification, since they vary greatly between species in number, color, size, shape and hardness, as well as in whether all the spines produced by an areole are similar or whether they are of distinct kinds. Most spines are straight or at most slightly curved, and are described as hair-like, bristle-like, needle-like or awl-like, depending on their length and thickness. Some cacti have flattened spines (e.g. '' Sclerocactus papyracanthus''). Other cacti have hooked spines. Sometimes, one or more central spines are hooked, while outer spines are straight (e.g., '' Mammillaria rekoi''). In addition to normal-length spines, members of the subfamily Opuntioideae have relatively short spines, called
glochid Glochids or glochidia (singular "glochidium") are hair-like spines or short prickles, generally barbed, found on the areoles of cacti in the sub-family ''Opuntioideae''. Cactus glochids easily detach from the plant and lodge in the skin, causin ...
s, that are barbed along their length and easily shed. These enter the skin and are difficult to remove due to being very fine and easily broken, causing long-lasting irritation. Ferocactus1001.jpg, Varied spines of a ''
Ferocactus ''Ferocactus'' is a genus of large barrel-shaped cacti, mostly with large spines and small flowers. There are about 30 species included in the genus. They are found in the southwestern United States and northwestern Mexico. Description The y ...
'' Hakendornen IMGP7026 WP.jpg, Hooked central spine (cf. '' Mammillaria rekoi'') Toumeya papyracantha fh 087 3 AZ BB.jpg, Unusual flattened spines of '' Sclerocactus papyracanthus'' Opuntia microdasys 01 ies cropped.jpg, Glochids of ''
Opuntia microdasys ''Opuntia microdasys'' (angel's-wings, bunny ears cactus, bunny cactus or polka-dot cactus) is a species of flowering plant in the cactus family Cactaceae, native and endemic to central and northern Mexico. Description ''Opuntia microdasys'' fo ...
''


Roots

Most ground-living cacti have only fine roots, which spread out around the base of the plant for varying distances, close to the surface. Some cacti have taproots; in genera such as ''
Ariocarpus ''Ariocarpus'' is a small genus of succulent, subtropical plants of the family Cactaceae. The name comes from the ancient Greek "aria" (an oak type) and "carpos" (=fruit) because of the resemblance of the fruit of the two genus in acorn for ...
'', these are considerably larger and of a greater volume than the body. Taproots may aid in stabilizing the larger columnar cacti. Climbing, creeping and epiphytic cacti may have only
adventitious roots Important structures in plant development are buds, shoots, roots, leaves, and flowers; plants produce these tissues and structures throughout their life from meristems located at the tips of organs, or between mature tissues. Thus, a living plant ...
, produced along the stems where these come into contact with a rooting medium.


Flowers

Like their spines, cactus flowers are variable. Typically, the
ovary The ovary is an organ in the female reproductive system that produces an ovum. When released, this travels down the fallopian tube into the uterus, where it may become fertilized by a sperm. There is an ovary () found on each side of the body. ...
is surrounded by material derived from stem or receptacle tissue, forming a structure called a pericarpel. Tissue derived from the
petals Petals are modified leaves that surround the reproductive parts of flowers. They are often brightly colored or unusually shaped to attract pollinators. All of the petals of a flower are collectively known as the ''corolla''. Petals are usually ...
and sepals continues the pericarpel, forming a composite tube—the whole may be called a floral tube, although strictly speaking only the part furthest from the base is floral in origin. The outside of the tubular structure often has
areoles In botany, areoles are small light- to dark-colored bumps on cacti out of which grow clusters of spines. Areoles are important diagnostic features of cacti, and identify them as a family distinct from other succulent plants. Gordon Rowley - Wh ...
that produce wool and spines. Typically, the tube also has small scale-like bracts, which gradually change into sepal-like and then petal-like structures, so the sepals and petals cannot be clearly differentiated (and hence are often called " tepals"). Some cacti produce floral tubes without wool or spines (e.g. ''
Gymnocalycium ''Gymnocalycium'', commonly called chin cactus, is a genus of about 70 South American species of cactus. The genus name ''Gymnocalycium'' (from Greek, "naked calyx") refers to the flower buds bearing no hair or spines. Their main area of distrib ...
'') or completely devoid of any external structures (e.g. ''
Mammillaria ''Mammillaria'' is one of the largest genera in the cactus family (Cactaceae), with currently 200 known species and varieties recognized. Most of the mammillaria are native to Mexico, but some come from the southwest United States, the Caribb ...
''). Unlike the flowers of most other cacti, ''
Pereskia ''Pereskia'' is a small genus of about four species of cacti that do not look much like other types of cacti, having substantial leaves and non-succulent stems. The genus is named after Nicolas-Claude Fabri de Peiresc, a 16th-century French bota ...
'' flowers may be borne in clusters. Cactus flowers usually have many stamens, but only a single style, which may branch at the end into more than one stigma. The stamens usually arise from all over the inner surface of the upper part of the floral tube, although in some cacti, the stamens are produced in one or more distinct "series" in more specific areas of the inside of the floral tube. The flower as a whole is usually radially symmetrical (
actinomorphic Floral symmetry describes whether, and how, a flower, in particular its perianth, can be divided into two or more identical or mirror-image parts. Uncommonly, flowers may have no axis of symmetry at all, typically because their parts are spirall ...
), but may be bilaterally symmetrical (
zygomorphic Floral symmetry describes whether, and how, a flower, in particular its perianth, can be divided into two or more identical or mirror-image parts. Uncommonly, flowers may have no axis of symmetry at all, typically because their parts are spirall ...
) in some species. Flower colors range from white through yellow and red to magenta.


Adaptations for water conservation

All cacti have some adaptations to promote efficient water use. Most cacti— opuntias and cactoids—specialize in surviving in hot and dry environments (i.e. are
xerophytes A xerophyte (from Greek ξηρός ''xeros'' 'dry' + φυτόν ''phuton'' 'plant') is a species of plant that has adaptations to survive in an environment with little liquid water, such as a desert such as the Sahara or places in the Alps or the ...
), but the first ancestors of modern cacti were already adapted to periods of intermittent drought. A small number of cactus species in the tribes
Hylocereeae The Hylocereeae are a tribe of cacti. Most are found in the tropical forests of Central and northern South America, and are climbers or epiphytes, unlike most cacti. The tribe includes between six and eight genera in different circumscriptio ...
and
Rhipsalideae The Rhipsalideae are a small tribe of cacti, comprising four genera (and around 60 species). They grow on trees ( epiphytes) or on rocks (lithophytes), where they either hang down or form creeping or upright shrubs. Their flowers open in the da ...
have become adapted to life as climbers or
epiphyte An epiphyte is an organism that grows on the surface of a plant and derives its moisture and nutrients from the air, rain, water (in marine environments) or from debris accumulating around it. The plants on which epiphytes grow are called phoroph ...
s, often in tropical forests, where water conservation is less important.


Leaves and spines

The absence of visible leaves is one of the most striking features of most cacti. ''
Pereskia ''Pereskia'' is a small genus of about four species of cacti that do not look much like other types of cacti, having substantial leaves and non-succulent stems. The genus is named after Nicolas-Claude Fabri de Peiresc, a 16th-century French bota ...
'' (which is close to the ancestral species from which all cacti evolved) does have long-lasting leaves, which are, however, thickened and succulent in many species. Other species of cactus with long-lasting leaves, such as the opuntioid ''
Pereskiopsis ''Pereskiopsis'' is a genus of cactus (family Cactaceae) in the subfamily Opuntioideae. Unlike typical cacti, it has persistent fleshy leaves. The genus name refers to its resemblance to the genus '' Pereskia''. Most species are found in Mexico ...
'', also have succulent leaves. A key issue in retaining water is the ratio of surface area to volume. Water loss is proportional to surface area, whereas the amount of water present is proportional to volume. Structures with a high surface area-to-volume ratio, such as thin leaves, necessarily lose water at a higher rate than structures with a low area-to-volume ratio, such as thickened stems. Spines, which are modified leaves, are present on even those cacti with true leaves, showing the evolution of spines preceded the loss of leaves. Although spines have a high surface area-to-volume ratio, at maturity they contain little or no water, being composed of fibers made up of dead cells. Spines provide protection from
herbivore A herbivore is an animal anatomically and physiologically adapted to eating plant material, for example foliage or marine algae, for the main component of its diet. As a result of their plant diet, herbivorous animals typically have mouthp ...
s and camouflage in some species, and assist in water conservation in several ways. They trap air near the surface of the cactus, creating a moister layer that reduces evaporation and transpiration. They can provide some shade, which lowers the temperature of the surface of the cactus, also reducing water loss. When sufficiently moist air is present, such as during fog or early morning mist, spines can condense moisture, which then drips onto the ground and is absorbed by the roots.


Stems

The majority of cacti are stem succulents, i.e., plants in which the stem is the main organ used to store water. Water may form up to 90% of the total mass of a cactus. Stem shapes vary considerably among cacti. The cylindrical shape of columnar cacti and the spherical shape of globular cacti produce a low surface area-to-volume ratio, thus reducing water loss, as well as minimizing the heating effects of sunlight. The ribbed or fluted stems of many cacti allow the stem to shrink during periods of drought and then swell as it fills with water during periods of availability. A mature saguaro (''
Carnegiea gigantea The saguaro (, ) (''Carnegiea gigantea'') is a tree-like cactus species in the monotypic genus ''Carnegiea'' that can grow to be over tall. It is native to the Sonoran Desert in Arizona, the Mexican state of Sonora, and the Whipple Mountains ...
'') is said to be able to absorb as much as of water during a rainstorm. The outer layer of the stem usually has a tough
cuticle A cuticle (), or cuticula, is any of a variety of tough but flexible, non-mineral outer coverings of an organism, or parts of an organism, that provide protection. Various types of "cuticle" are non- homologous, differing in their origin, structu ...
, reinforced with waxy layers, which reduce water loss. These layers are responsible for the grayish or bluish tinge to the stem color of many cacti. The stems of most cacti have adaptations to allow them to conduct photosynthesis in the absence of leaves. This is discussed further below under Metabolism.


Roots

Many cacti have roots that spread out widely, but only penetrate a short distance into the soil. In one case, a young saguaro only tall had a root system with a diameter of , but no more than deep. Cacti can also form new roots quickly when rain falls after a drought. The concentration of salts in the root cells of cacti is relatively high. All these adaptations enable cacti to absorb water rapidly during periods of brief or light rainfall. Thus, ''
Ferocactus cylindraceus ''Ferocactus cylindraceus'' is a species of barrel cactus which is known by several common names, including California barrel cactus, Desert barrel cactus, and miner's compass. It was first described by George Engelmann in 1853. Distribution an ...
'' reportedly can take up a significant amount of water within 12 hours from as little as of rainfall, becoming fully hydrated in a few days. Although in most cacti, the stem acts as the main organ for storing water, some cacti have in addition large
taproots A taproot is a large, central, and dominant root from which other roots sprout laterally. Typically a taproot is somewhat straight and very thick, is tapering in shape, and grows directly downward. In some plants, such as the carrot, the taproo ...
. These may be several times the length of the above-ground body in the case of species such as '' Copiapoa atacamensis'', which grows in one of the driest places in the world, the
Atacama Desert The Atacama Desert ( es, Desierto de Atacama) is a desert plateau in South America covering a 1,600 km (990 mi) strip of land on the Pacific coast, west of the Andes Mountains. The Atacama Desert is the driest nonpolar desert in the w ...
in northern Chile.


Metabolism

Photosynthesis requires plants to take in carbon dioxide gas (). As they do so, they lose water through transpiration. Like other types of
succulents In botany, succulent plants, also known as succulents, are plants with parts that are thickened, fleshy, and engorged, usually to retain water in arid climates or soil conditions. The word ''succulent'' comes from the Latin word ''sucus'', meani ...
, cacti reduce this water loss by the way in which they carry out photosynthesis. "Normal" leafy plants use the C3 mechanism: during daylight hours, is continually drawn out of the air present in spaces inside leaves and converted first into a compound containing three carbon atoms (
3-phosphoglycerate 3-Phosphoglyceric acid (3PG, 3-PGA, or PGA) is the conjugate acid of 3-phosphoglycerate or glycerate 3-phosphate (GP or G3P). This glycerate is a biochemically significant metabolic intermediate in both glycolysis and the Calvin-Benson cycle. The ...
) and then into products such as carbohydrates. The access of air to internal spaces within a plant is controlled by
stoma In botany, a stoma (from Greek ''στόμα'', "mouth", plural "stomata"), also called a stomate (plural "stomates"), is a pore found in the epidermis of leaves, stems, and other organs, that controls the rate of gas exchange. The pore is bor ...
ta, which are able to open and close. The need for a continuous supply of during photosynthesis means the stomata must be open, so water vapor is continuously being lost. Plants using the C3 mechanism lose as much as 97% of the water taken up through their roots in this way. A further problem is that as temperatures rise, the enzyme that captures starts to capture more and more oxygen instead, reducing the efficiency of photosynthesis by up to 25%.
Crassulacean acid metabolism Crassulacean acid metabolism, also known as CAM photosynthesis, is a carbon fixation pathway that evolved in some plants as an adaptation to arid conditions that allows a plant to photosynthesize during the day, but only exchange gases at night. I ...
(CAM) is a mechanism adopted by cacti and other succulents to avoid the problems of the C3 mechanism. In full CAM, the stomata open only at night, when temperatures and water loss are lowest. enters the plant and is captured in the form of organic acids stored inside cells (in
vacuole A vacuole () is a membrane-bound organelle which is present in plant and fungal cells and some protist, animal, and bacterial cells. Vacuoles are essentially enclosed compartments which are filled with water containing inorganic and organic mo ...
s). The stomata remain closed throughout the day, and photosynthesis uses only this stored . CAM uses water much more efficiently at the price of limiting the amount of carbon fixed from the atmosphere and thus available for growth. CAM-cycling is a less water-efficient system whereby stomata open in the day, just as in plants using the C3 mechanism. At night, or when the plant is short of water, the stomata close and the CAM mechanism is used to store produced by respiration for use later in photosynthesis. CAM-cycling is present in ''Pereskia'' species. By studying the ratio of 14C to 13C incorporated into a plant—its isotopic signature—it is possible to deduce how much is taken up at night and how much in the daytime. Using this approach, most of the ''Pereskia'' species investigated exhibit some degree of CAM-cycling, suggesting this ability was present in the ancestor of all cacti. ''Pereskia'' leaves are claimed to only have the C3 mechanism with CAM restricted to stems. More recent studies show that "it is highly unlikely that significant carbon assimilation occurs in the stem"; ''Pereskia'' species are described as having "C3 with inducible CAM." Leafless cacti carry out all their photosynthesis in the stem, using full CAM. , it is not clear whether stem-based CAM evolved once only in the core cacti, or separately in the opuntias and cactoids; CAM is known to have evolved convergently many times. To carry out photosynthesis, cactus stems have undergone many adaptations. Early in their evolutionary history, the ancestors of modern cacti (other than ''Leuenbergeria'' species) developed
stoma In botany, a stoma (from Greek ''στόμα'', "mouth", plural "stomata"), also called a stomate (plural "stomates"), is a pore found in the epidermis of leaves, stems, and other organs, that controls the rate of gas exchange. The pore is bor ...
ta on their stems and began to delay developing bark. However, this alone was not sufficient; cacti with only these adaptations appear to do very little photosynthesis in their stems. Stems needed to develop structures similar to those normally found only in leaves. Immediately below the outer epidermis, a hypodermal layer developed made up of cells with thickened walls, offering mechanical support. Air spaces were needed between the cells to allow carbon dioxide to diffuse inwards. The center of the stem, the cortex, developed "
chlorenchyma The ground tissue of plants includes all tissues that are neither dermal nor vascular. It can be divided into three types based on the nature of the cell walls. # Parenchyma cells have thin primary walls and usually remain alive after they beco ...
" – a plant tissue made up of relatively unspecialized cells containing
chloroplast A chloroplast () is a type of membrane-bound organelle known as a plastid that conducts photosynthesis mostly in plant and algal cells. The photosynthetic pigment chlorophyll captures the energy from sunlight, converts it, and stores it in ...
s, arranged into a "spongy layer" and a " palisade layer" where most of the photosynthesis occurs.


Taxonomy and classification

Naming and classifying cacti has been both difficult and controversial since the first cacti were discovered for science. The difficulties began with Carl Linnaeus. In 1737, he placed the cacti he knew into two genera, ''Cactus'' and ''Pereskia''. However, when he published '' Species Plantarum'' in 1753—the starting point for modern botanical nomenclature—he relegated them all to one genus, ''Cactus''. The word "cactus" is derived through Latin from the Ancient Greek (''kaktos''), a name used by Theophrastus for a spiny plant, which may have been the
cardoon The cardoon, ''Cynara cardunculus'' (), also called the artichoke thistle, is a thistle in the family Asteraceae. It is a naturally occurring species that also has many cultivated forms, including the globe artichoke. It is native to the wester ...
(''Cynara cardunculus''). Later botanists, such as Philip Miller in 1754, divided cacti into several genera, which, in 1789,
Antoine Laurent de Jussieu Antoine Laurent de Jussieu (; 12 April 1748 – 17 September 1836) was a French botanist, notable as the first to publish a natural classification of flowering plants; much of his system remains in use today. His classification was based on an e ...
placed in his newly created family Cactaceae. By the early 20th century, botanists came to feel Linnaeus's name ''Cactus'' had become so confused as to its meaning (was it the genus or the family?) that it should not be used as a genus name. The 1905 Vienna botanical congress rejected the name ''Cactus'' and instead declared ''Mammillaria'' was the type genus of the family Cactaceae. It did, however, conserve the name Cactaceae, leading to the unusual situation in which the family Cactaceae no longer contains the genus after which it was named. The difficulties continued, partly because giving plants scientific names relies on "
type specimens In biology, a type is a particular specimen (or in some cases a group of specimens) of an organism to which the scientific name of that organism is formally attached. In other words, a type is an example that serves to anchor or centralizes the ...
". Ultimately, if botanists want to know whether a particular plant is an example of, say, ''Mammillaria mammillaris'', they should be able to compare it with the type specimen to which this name is permanently attached. Type specimens are normally prepared by compression and drying, after which they are stored in
herbaria A herbarium (plural: herbaria) is a collection of preserved plant specimens and associated data used for scientific study. The specimens may be whole plants or plant parts; these will usually be in dried form mounted on a sheet of paper (called ...
to act as definitive references. However, cacti are very difficult to preserve in this way; they have evolved to resist drying and their bodies do not easily compress. A further difficulty is that many cacti were given names by growers and horticulturalists rather than botanists; as a result, the provisions of the ''
International Code of Nomenclature for algae, fungi, and plants The ''International Code of Nomenclature for algae, fungi, and plants'' (ICN) is the set of rules and recommendations dealing with the formal botanical names that are given to plants, fungi and a few other groups of organisms, all those "tra ...
'' (which governs the names of cacti, as well as other plants) were often ignored.
Curt Backeberg Curt Backeberg (2 August 1894 in Lüneburg, Germany – 14 January 1966) was a German horticulturist especially known for the collection and classification of cacti. Biography He travelled extensively through Central and South America, and publis ...
, in particular, is said to have named or renamed 1,200 species without one of his names ever being attached to a specimen, which, according to David Hunt, ensured he "left a trail of nomenclatural chaos that will probably vex cactus taxonomists for centuries."


Classification

In 1984, it was decided that the Cactaceae Section of the
International Organization for Succulent Plant Study The International Organization for Succulent Plant Study (IOS) describes itself as a "non-governmental organization promoting the study and conservation of succulent and allied plants and encouraging collaboration among scientists and curators ...
should set up a working party, now called the International Cactaceae Systematics Group (ICSG), to produce consensus classifications down to the level of genera. Their system has been used as the basis of subsequent classifications. Detailed treatments published in the 21st century have divided the family into around 125–130 genera and 1,400–1,500 species, which are then arranged into a number of tribes and subfamilies. The ICSG classification of the cactus family recognized four subfamilies, the largest of which was divided into nine tribes. The subfamilies were: * Subfamily Pereskioideae K. Schumann :The only genus in the ICSG classification was ''Pereskia''. It has features considered closest to the ancestors of the Cactaceae. Plants are trees or shrubs with leaves; their stems are smoothly round in cross section, rather than being ribbed or having tubercles. Two systems may be used in photosynthesis, both the "normal" C3 mechanism and crassulean acid metabolism (CAM)—an "advanced" feature of cacti and other
succulents In botany, succulent plants, also known as succulents, are plants with parts that are thickened, fleshy, and engorged, usually to retain water in arid climates or soil conditions. The word ''succulent'' comes from the Latin word ''sucus'', meani ...
that conserves water. :
Molecular phylogenetic Molecular phylogenetics () is the branch of phylogeny that analyzes genetic, hereditary molecular differences, predominantly in DNA sequences, to gain information on an organism's evolutionary relationships. From these analyses, it is possible to ...
studies showed that when broadly circumscribed, ''Pereskia'' was not monophyletic, and it has been split into three genera, ''
Leuenbergeria ''Leuenbergeria '' is a genus of flowering plant in the family Cactaceae, mostly native around the Caribbean. Unlike most cacti, it has persistent leaves and develops bark on its stems early in its growth. The genus was created in 2012 by Joël L ...
'', ''
Rhodocactus ''Rhodocactus'' is a genus of flowering plant in the cactus family Cactaceae, native to central South America. Unlike most species of cacti, ''Rhodocactus'' has persistent leaves and a fully tree-like habit. The genus was sunk into a broadly ...
'' and a narrowly circumscribed ''
Pereskia ''Pereskia'' is a small genus of about four species of cacti that do not look much like other types of cacti, having substantial leaves and non-succulent stems. The genus is named after Nicolas-Claude Fabri de Peiresc, a 16th-century French bota ...
''. ''Leuenbergeria'' is then placed on its own in a separate monogeneric subfamily, Leuenbergerioideae. * Subfamily
Opuntioideae Opuntioideae is a subfamily of the cactus family, Cactaceae. It contains 15 genera divided into five tribes. The subfamily encompasses roughly 220–250 species, and is geographically distributed throughout the New World from Canada, to Argentina ...
K. Schumann :Some 15 genera are included in this subfamily. They may have leaves when they are young, but these are lost later. Their stems are usually divided into distinct "joints" or "pads" (
cladode Phylloclades and cladodes are flattened, photosynthetic shoots, which are usually considered to be modified branches. The two terms are used either differently or interchangeably by different authors. ''Phyllocladus'', a genus of conifer, is name ...
s). Plants vary in size from the small cushions of ''
Maihueniopsis ''Maihueniopsis'' (from Greek ''opsis'', "view", referring to its resemblance to the unrelated ''Maihuenia'') is a genus of the cactus family (Cactaceae), containing 18 species. The former genus ''Puna'' R.Kiesling is now synonym to ''Maihue ...
'' to treelike species of ''Opuntia'', rising to or more. * Subfamily
Maihuenioideae ''Maihuenia'' is a genus of cactus (family Cactaceae) and the sole genus of the subfamily Maihuenioideae, which is the smallest subfamily of the Cactaceae. The genus comprises two cushion-forming, mucilaginous species. They are found at high elev ...
P. Fearn :The only genus is ''Maihuenia'', with two species, both of which form low-growing mats. It has some features that are primitive within the cacti. Plants have leaves, and crassulean acid metabolism is wholly absent. * Subfamily
Cactoideae The Cactoideae are the largest subfamily of the cactus family, Cactaceae. Around 80% of cactus species belong to this subfamily. , the internal classification of the family Cactaceae remained uncertain and subject to change. A classification inc ...
:Divided into nine tribes, this is the largest subfamily, including all the "typical" cacti. Members are highly variable in habit, varying from tree-like to epiphytic. Leaves are normally absent, although sometimes very reduced leaves are produced by young plants. Stems are usually not divided into segments, and are ribbed or tuberculate. Two of the tribes,
Hylocereeae The Hylocereeae are a tribe of cacti. Most are found in the tropical forests of Central and northern South America, and are climbers or epiphytes, unlike most cacti. The tribe includes between six and eight genera in different circumscriptio ...
and
Rhipsalideae The Rhipsalideae are a small tribe of cacti, comprising four genera (and around 60 species). They grow on trees ( epiphytes) or on rocks (lithophytes), where they either hang down or form creeping or upright shrubs. Their flowers open in the da ...
, contain climbing or epiphytic forms with a rather different appearance; their stems are flattened and may be divided into segments. Molecular phylogenetic studies have supported the monophyly of three of these subfamilies (not Pereskioideae), but have not supported all of the tribes or even genera below this level; indeed, a 2011 study found only 39% of the genera in the subfamily Cactoideae sampled in the research were monophyletic. Classification of the cacti currently remains uncertain and is likely to change.


Phylogeny and evolution


Phylogeny

A 2005 study suggested the genus ''
Pereskia ''Pereskia'' is a small genus of about four species of cacti that do not look much like other types of cacti, having substantial leaves and non-succulent stems. The genus is named after Nicolas-Claude Fabri de Peiresc, a 16th-century French bota ...
'' as then circumscribed (''Pereskia'' sensu lato) was basal within the Cactaceae, but confirmed earlier suggestions it was not monophyletic, i.e., did not include all the descendants of a common ancestor. The
Bayesian Thomas Bayes (/beɪz/; c. 1701 – 1761) was an English statistician, philosopher, and Presbyterian minister. Bayesian () refers either to a range of concepts and approaches that relate to statistical methods based on Bayes' theorem, or a follower ...
consensus
cladogram A cladogram (from Greek ''clados'' "branch" and ''gramma'' "character") is a diagram used in cladistics to show relations among organisms. A cladogram is not, however, an evolutionary tree because it does not show how ancestors are related to ...
from this study is shown below with subsequent generic changes added. A 2011 study using fewer genes but more species also found that ''Pereskia'' s.l. was divided into the same clades, but was unable to resolve the members of the "core cacti" clade. It was accepted that the relationships shown above are "the most robust to date." ''
Leuenbergeria ''Leuenbergeria '' is a genus of flowering plant in the family Cactaceae, mostly native around the Caribbean. Unlike most cacti, it has persistent leaves and develops bark on its stems early in its growth. The genus was created in 2012 by Joël L ...
'' species (''Pereskia'' s.l. Clade A) always lack two key features of the stem present in most of the remaining "caulocacti": like most non-cacti, their stems begin to form
bark Bark may refer to: * Bark (botany), an outer layer of a woody plant such as a tree or stick * Bark (sound), a vocalization of some animals (which is commonly the dog) Places * Bark, Germany * Bark, Warmian-Masurian Voivodeship, Poland Arts, e ...
early in the plants' life and also lack
stoma In botany, a stoma (from Greek ''στόμα'', "mouth", plural "stomata"), also called a stomate (plural "stomates"), is a pore found in the epidermis of leaves, stems, and other organs, that controls the rate of gas exchange. The pore is bor ...
ta—structures that control admission of air into a plant and hence control photosynthesis. By contrast, caulocacti, including species of ''
Rhodocactus ''Rhodocactus'' is a genus of flowering plant in the cactus family Cactaceae, native to central South America. Unlike most species of cacti, ''Rhodocactus'' has persistent leaves and a fully tree-like habit. The genus was sunk into a broadly ...
'' and the remaining species of ''Pereskia'' s.s., typically delay forming bark and have stomata on their stems, thus giving the stem the potential to become a major organ for photosynthesis. (The two highly specialized species of ''
Maihuenia ''Maihuenia'' is a genus of cactus (family Cactaceae) and the sole genus of the subfamily Maihuenioideae, which is the smallest subfamily of the Cactaceae. The genus comprises two cushion-forming, mucilaginous species. They are found at high elev ...
'' are something of an exception.) The first cacti are thought to have been only slightly succulent shrubs or small trees whose leaves carried out photosynthesis. They lived in tropical areas that experienced periodic drought. If ''Leuenbergeria'' is a good model of these early cacti, then, although they would have appeared superficially similar to other trees growing nearby, they had already evolved strategies to conserve water (some of which are present in members of other families in the order
Caryophyllales Caryophyllales ( ) is a diverse and heterogeneous order of flowering plants that includes the cacti, carnations, amaranths, ice plants, beets, and many carnivorous plants. Many members are succulent, having fleshy stems or leaves. The betala ...
). These strategies included being able to respond rapidly to periods of rain, and keeping transpiration low by using water very efficiently during photosynthesis. The latter was achieved by tightly controlling the opening of stomata. Like ''Pereskia'' species today, early ancestors may have been able to switch from the normal C3 mechanism, where carbon dioxide is used continuously in photosynthesis, to CAM cycling, in which when the stomata are closed, carbon dioxide produced by respiration is stored for later use in photosynthesis. The clade containing ''Rhodocactus'' and ''Pereskia'' s.s. marks the beginnings of an evolutionary switch to using stems as photosynthetic organs. Stems have stomata and the formation of bark takes place later than in normal trees. The "core cacti" show a steady increase in both stem succulence and photosynthesis accompanied by multiple losses of leaves, more-or-less complete in the Cactoideae. One evolutionary question at present unanswered is whether the switch to full CAM photosynthesis in stems occurred only once in the core cacti, in which case it has been lost in ''Maihuenia'', or separately in Opuntioideae and Cactoideae, in which case it never evolved in ''Maihuenia''. Understanding evolution within the core cacti clade is difficult , since phylogenetic relationships are still uncertain and not well related to current classifications. Thus, a 2011 study found "an extraordinarily high proportion of genera" were not monophyletic, so were not all descendants of a single common ancestor. For example, of the 36 genera in the subfamily Cactoideae sampled in the research, 22 (61%) were found not monophyletic. Nine tribes are recognized within Cactoideae in the International Cactaceae Systematics Group (ICSG) classification; one, Calymmantheae, comprises a single genus, ''Calymmanthium''. Only two of the remaining eight – Cacteae and Rhipsalideae – were shown to be monophyletic in a 2011 study by Hernández-Hernández et al. For a more detailed discussion of the phylogeny of the cacti, see
Classification of the Cactaceae In 1984, the International Organization for Succulent Plant Study set up a working party, now called the International Cactaceae Systematics Group, to produce a consensus classification of the cactus family, down to the level of genus. Their clas ...
.


Evolutionary history

No known fossils of cacti exist to throw light on their evolutionary history. However, the geographical distribution of cacti offers some evidence. Except for a relatively recent spread of ''
Rhipsalis baccifera ''Rhipsalis baccifera'', commonly known as the mistletoe cactus, is an epiphytic cactus which originates from Central and South America, the Caribbean, and Florida. It is also found throughout the tropics of Africa and into Sri Lanka where it ...
'' to parts of the
Old World The "Old World" is a term for Afro-Eurasia that originated in Europe , after Europeans became aware of the existence of the Americas. It is used to contrast the continents of Africa, Europe, and Asia, which were previously thought of by th ...
, cacti are plants of South America and mainly southern regions of North America. This suggests the family must have evolved after the ancient continent of Gondwana split into South America and
Africa Africa is the world's second-largest and second-most populous continent, after Asia in both cases. At about 30.3 million km2 (11.7 million square miles) including adjacent islands, it covers 6% of Earth's total surface area ...
, which occurred during the Early Cretaceous, around . Precisely when after this split cacti evolved is less clear. Older sources suggest an early origin around 90 – 66 million years ago, during the Late Cretaceous. More recent molecular studies suggest a much younger origin, perhaps in very Late Eocene to early Oligocene periods, around 35–30 million years ago. Based on the phylogeny of the cacti, the earliest diverging group (''Leuenbergeria'') may have originated in Central America and northern South America, whereas the caulocacti, those with more-or-less succulent stems, evolved later in the southern part of South America, and then moved northwards. Core cacti, those with strongly succulent stems, are estimated to have evolved around 25 million years ago. A possible stimulus to their evolution may have been uplifting in the central Andes, some 25–20 million years ago, which was associated with increasing and varying aridity. However, the current species diversity of cacti is thought to have arisen only in the last 10–5 million years (from the late Miocene into the Pliocene). Other succulent plants, such as the
Aizoaceae The Aizoaceae, or fig-marigold family, is a large family of dicotyledonous flowering plants containing 135 genera and about 1800 species. They are commonly known as ice plants or carpet weeds. They are often called vygies in South Africa and N ...
in South Africa, the
Didiereaceae Didiereaceae is a family of flowering plants found in continental Africa and Madagascar. It contains 20 species classified in three subfamilies and six genera. Species of the family are succulent plants, growing in sub-arid to arid habitats. Seve ...
in Madagascar and the genus ''
Agave ''Agave'' (; ; ) is a genus of monocots native to the hot and arid regions of the Americas and the Caribbean, although some ''Agave'' species are also native to tropical areas of North America, such as Mexico. The genus is primarily known for i ...
'' in the Americas, appear to have diversified at the same time, which coincided with a global expansion of arid environments.


Distribution

Cacti inhabit diverse regions, from coastal plains to high mountain areas. With one exception, they are native to the
Americas The Americas, which are sometimes collectively called America, are a landmass comprising the totality of North and South America. The Americas make up most of the land in Earth's Western Hemisphere and comprise the New World. Along with t ...
, where their range extends from Patagonia to British Columbia and
Alberta Alberta ( ) is one of the thirteen provinces and territories of Canada. It is part of Western Canada and is one of the three prairie provinces. Alberta is bordered by British Columbia to the west, Saskatchewan to the east, the Northwest Terri ...
in western Canada. A number of centers of diversity exist. For cacti adapted to drought, the three main centers are Mexico and the southwestern United States; the southwestern Andes, where they are found in Peru,
Bolivia , image_flag = Bandera de Bolivia (Estado).svg , flag_alt = Horizontal tricolor (red, yellow, and green from top to bottom) with the coat of arms of Bolivia in the center , flag_alt2 = 7 × 7 square p ...
,
Chile Chile, officially the Republic of Chile, is a country in the western part of South America. It is the southernmost country in the world, and the closest to Antarctica, occupying a long and narrow strip of land between the Andes to the east a ...
and
Argentina Argentina (), officially the Argentine Republic ( es, link=no, República Argentina), is a country in the southern half of South America. Argentina covers an area of , making it the second-largest country in South America after Brazil, th ...
; and eastern Brazil, away from the
Amazon Basin The Amazon basin is the part of South America drained by the Amazon River and its tributaries. The Amazon drainage basin covers an area of about , or about 35.5 percent of the South American continent. It is located in the countries of Boliv ...
. Tree-living epiphytic and climbing cacti necessarily have different centers of diversity, as they require moister environments. They are mainly found in the coastal mountains and Atlantic forests of southeastern Brazil; in Bolivia, which is the center of diversity for the subfamily
Rhipsalideae The Rhipsalideae are a small tribe of cacti, comprising four genera (and around 60 species). They grow on trees ( epiphytes) or on rocks (lithophytes), where they either hang down or form creeping or upright shrubs. Their flowers open in the da ...
; and in forested regions of
Central America Central America ( es, América Central or ) is a subregion of the Americas. Its boundaries are defined as bordering the United States to the north, Colombia to the south, the Caribbean Sea to the east, and the Pacific Ocean to the west. C ...
, where the climbing
Hylocereeae The Hylocereeae are a tribe of cacti. Most are found in the tropical forests of Central and northern South America, and are climbers or epiphytes, unlike most cacti. The tribe includes between six and eight genera in different circumscriptio ...
are most diverse. ''
Rhipsalis baccifera ''Rhipsalis baccifera'', commonly known as the mistletoe cactus, is an epiphytic cactus which originates from Central and South America, the Caribbean, and Florida. It is also found throughout the tropics of Africa and into Sri Lanka where it ...
'' is the exception; it is native to both the Americas and the
Old World The "Old World" is a term for Afro-Eurasia that originated in Europe , after Europeans became aware of the existence of the Americas. It is used to contrast the continents of Africa, Europe, and Asia, which were previously thought of by th ...
, where it is found in tropical
Africa Africa is the world's second-largest and second-most populous continent, after Asia in both cases. At about 30.3 million km2 (11.7 million square miles) including adjacent islands, it covers 6% of Earth's total surface area ...
, Madagascar, and Sri Lanka. One theory is it was spread by being carried as seeds in the
digestive tract The gastrointestinal tract (GI tract, digestive tract, alimentary canal) is the tract or passageway of the digestive system that leads from the mouth to the anus. The GI tract contains all the major organs of the digestive system, in humans and ...
s of migratory birds; the seeds of ''Rhipsalis'' are adapted for bird distribution. Old World populations are
polyploid Polyploidy is a condition in which the cells of an organism have more than one pair of ( homologous) chromosomes. Most species whose cells have nuclei ( eukaryotes) are diploid, meaning they have two sets of chromosomes, where each set conta ...
, and regarded as distinct subspecies, supporting the idea that the spread was not recent. The alternative theory is the species initially crossed the Atlantic on European ships trading between South America and Africa, after which birds may have spread it more widely.


Naturalized species

Many other species have become naturalized outside the Americas after having been introduced by people, especially in Australia, Hawaii, and the Mediterranean region. In Australia, species of '' Opuntia'', particularly ''
Opuntia stricta ''Opuntia stricta'' is a species of large cactus that is endemic to the subtropical and tropical coastal areas of the Americas, especially around the Caribbean. Common names include erect prickly pear and nopal estricto (Spanish). The first desc ...
'', were introduced in the 19th century for use as natural agricultural fences and in an attempt to establish a
cochineal The cochineal ( , ; ''Dactylopius coccus'') is a scale insect in the suborder Sternorrhyncha, from which the natural dye carmine is derived. A primarily sessile parasite native to tropical and subtropical South America through North America ...
industry. They rapidly became a major weed problem, but are now controlled by biological agents, particularly the moth ''
Cactoblastis cactorum ''Cactoblastis cactorum'', the cactus moth, South American cactus moth or nopal moth, is native to Argentina, Paraguay, Uruguay and southern Brazil. It is one of five species in the genus '' Cactoblastis'' that inhabit South America, where many pa ...
''. The weed potential of Opuntia species in Australia continues however, leading to all opuntioid cacti except '' O. ficus-indica'' being declared Weeds of National Significance by the
Australian Weeds Committee Invasive species in Australia are a serious threat to the native biodiversity, and an ongoing cost to Australian agriculture. Numerous species arrived with European maritime exploration and colonisation of Australia and steadily since then. ...
in April 2012. The
Arabian Peninsula The Arabian Peninsula, (; ar, شِبْهُ الْجَزِيرَةِ الْعَرَبِيَّة, , "Arabian Peninsula" or , , "Island of the Arabs") or Arabia, is a peninsula of Western Asia, situated northeast of Africa on the Arabian Plate. ...
has a wide variety of ever-increasing, introduced cactus populations. Some of these are cultivated, some are escapes from cultivation, and some are invasives that are presumed to be ornamental escapes.


Reproductive ecology

Cactus flowers are
pollinated Pollination is the transfer of pollen from an anther of a plant to the stigma of a plant, later enabling fertilisation and the production of seeds, most often by an animal or by wind. Pollinating agents can be animals such as insects, birds, a ...
by insects, birds and bats. None are known to be wind-pollinated and self-pollination occurs in only a very few species; for example the flowers of some species of ''
Frailea ''Frailea'' is a genus of globular to short cylindrical cacti native to South America. These species are cleistogamous. They were first classified in the genus '' Echinocactus''. Species Species accepted by the Plants of the World Online P ...
'' do not open (
cleistogamy Cleistogamy is a type of automatic self-pollination of certain plants that can propagate by using non-opening, self-pollinating flowers. Especially well known in peanuts, peas, and pansies, this behavior is most widespread in the grass family. H ...
). The need to attract pollinators has led to the evolution of
pollination syndrome Pollination syndromes are suites of flower traits that have evolved in response to natural selection imposed by different pollen vectors, which can be abiotic (wind and water) or biotic, such as birds, bees, flies, and so forth through a process c ...
s, which are defined as groups of "floral traits, including rewards, associated with the attraction and utilization of a specific group of animals as pollinators."
Bee Bees are winged insects closely related to wasps and ants, known for their roles in pollination and, in the case of the best-known bee species, the western honey bee, for producing honey. Bees are a monophyletic lineage within the superfami ...
s are the most common pollinators of cacti; bee-pollination is considered to have been the first to evolve. Day-flying butterflies and nocturnal moths are associated with different pollination syndromes. Butterfly-pollinated flowers are usually brightly colored, opening during the day, whereas moth-pollinated flowers are often white or pale in color, opening only in the evening and at night. As an example, ''
Lophocereus schottii ''Lophocereus schottii'', the senita cactus, is a species of cactus from southern Arizona and north-western Mexico, particularly Baja California and Sonora. Synonyms include ''Pilocereus schottii'' and ''Pachycereus schottii''., pp. 536–537 Th ...
'' is pollinated by a particular species of moth, '' Upiga virescens'', which also lays its eggs among the developing seeds its caterpillars later consume. The flowers of this cactus are funnel-shaped, white to deep pink, up to long, and open at night. Hummingbirds are significant pollinators of cacti. Species showing the typical hummingbird-pollination syndrome have flowers with colors towards the red end of the spectrum, anthers and stamens that protrude from the flower, and a shape that is not
radially symmetrical Symmetry in biology refers to the symmetry observed in organisms, including plants, animals, fungi, and bacteria. External symmetry can be easily seen by just looking at an organism. For example, take the face of a human being which has a pl ...
, with a lower lip that bends downwards; they produce large amounts of nectar with a relatively low sugar content. ''
Schlumbergera ''Schlumbergera'' is a small genus of cacti with six to nine species found in the coastal mountains of south-eastern Brazil. These plants grow on trees or rocks in habitats that are generally shady with high humidity, and can be quite differen ...
'' species, such as '' S. truncata'', have flowers that correspond closely to this syndrome. Other hummingbird-pollinated genera include ''
Cleistocactus ''Cleistocactus'' is a genus of flowering plants in the cactus family Cactaceae, native to mountainous areas - to - of South America (Peru, Uruguay, Bolivia and Argentina). The name comes from the Greek ''kleistos'' meaning closed because the f ...
'' and ''
Disocactus ''Disocactus'' is a genus of epiphytic cacti in the tribe Hylocereeae found in Central America, the Caribbean and northern South America. It should not be confused with ''Discocactus'', which is a different genus. Species of ''Disocactus'' gr ...
''. Bat-pollination is relatively uncommon in flowering plants, but about a quarter of the genera of cacti are known to be pollinated by
bat Bats are mammals of the order Chiroptera.''cheir'', "hand" and πτερόν''pteron'', "wing". With their forelimbs adapted as wings, they are the only mammals capable of true and sustained flight. Bats are more agile in flight than most bi ...
s—an unusually high proportion, exceeded among
eudicots The eudicots, Eudicotidae, or eudicotyledons are a clade of flowering plants mainly characterized by having two seed leaves upon germination. The term derives from Dicotyledons. Traditionally they were called tricolpates or non-magnoliid dicot ...
by only two other families, both with very few genera. Columnar cacti growing in semidesert areas are among those most likely to be bat-pollinated; this may be because bats are able to travel considerable distances, so are effective pollinators of plants growing widely separated from one another. The pollination syndrome associated with bats includes a tendency for flowers to open in the evening and at night, when bats are active. Other features include a relatively dull color, often white or green; a radially symmetrical shape, often tubular; a smell described as "musty"; and the production of a large amount of sugar-rich nectar. ''
Carnegiea gigantea The saguaro (, ) (''Carnegiea gigantea'') is a tree-like cactus species in the monotypic genus ''Carnegiea'' that can grow to be over tall. It is native to the Sonoran Desert in Arizona, the Mexican state of Sonora, and the Whipple Mountains ...
'' is an example of a bat-pollinated cactus, as are many species of ''
Pachycereus ''Pachycereus'' is a genus of 9–12 species of large cacti native to Mexico and just into southern Arizona, United States. They form large shrubs or small trees up to 15 m tall, with stout stems up to 1 m in diameter. ''Pachycereus'' comes fro ...
'' and ''
Pilosocereus ''Pilosocereus'' (from Latin, "hairy cereus") is a genus of cactus native to the Neotropics. Tree cactus is a common name for ''Pilosocereus'' species. The commonly cultivated '' Pilosocereus pachycladus'' ( syn. ''Pilosocereus azureus'') is a b ...
''. The fruits produced by cacti after the flowers have been fertilized vary considerably; many are fleshy, although some are dry. All contain a large number of seeds. Fleshy, colorful and sweet-tasting fruits are associated with seed dispersal by birds. The seeds pass through their digestive systems and are deposited in their droppings. Fruit that falls to the ground may be eaten by other animals;
giant tortoises Giant tortoises are any of various large land tortoises Giant tortoise or giant tortoises may also refer to: * Galápagos giant tortoise, ''Chelonoidis nigra'' are a complex of the largest living species of tortoise. :: Pinta giant tortoise or ...
are reported to distribute ''Opuntia'' seeds in the Galápagos Islands.
Ant Ants are eusocial insects of the family Formicidae and, along with the related wasps and bees, belong to the order Hymenoptera. Ants evolved from vespoid wasp ancestors in the Cretaceous period. More than 13,800 of an estimated total of 22,0 ...
s appear to disperse the seeds of a few genera, such as ''
Blossfeldia ''Blossfeldia'' is a genus of cactus (family Cactaceae) containing only one species, ''Blossfeldia liliputiana'', native to South America in northwestern Argentina (Jujuy, Salta, Tucumán, Catamarca and Mendoza Provinces) and southern Bolivia ...
''. Drier spiny fruits may cling to the fur of mammals or be moved around by the wind.


Uses


Early history

, there is still controversy as to the precise dates when humans first entered those areas of the New World where cacti are commonly found, and hence when they might first have used them. An archaeological site in
Chile Chile, officially the Republic of Chile, is a country in the western part of South America. It is the southernmost country in the world, and the closest to Antarctica, occupying a long and narrow strip of land between the Andes to the east a ...
has been dated to around 15,000 years ago, suggesting cacti would have been encountered before then. Early evidence of the use of cacti includes cave paintings in the Serra da Capivara in Brazil, and seeds found in ancient middens (waste dumps) in Mexico and Peru, with dates estimated at 12,000–9,000 years ago. Hunter-gatherers likely collected cactus fruits in the wild and brought them back to their camps. It is not known when cacti were first cultivated. Opuntias (prickly pears) were used for a variety of purposes by the
Aztecs The Aztecs () were a Mesoamerican culture that flourished in central Mexico in the post-classic period from 1300 to 1521. The Aztec people included different ethnic groups of central Mexico, particularly those groups who spoke the Nahuatl l ...
, whose empire, lasting from the 14th to the 16th century, had a complex system of horticulture. Their capital from the 15th century was Tenochtitlan (now Mexico City); one explanation for the origin of the name is that it includes the Nahuatl word ''nōchtli'', referring to the fruit of an opuntia. The coat of arms of Mexico shows an eagle perched on a cactus while holding a snake, an image at the center of the myth of the founding of Tenochtitlan. The Aztecs symbolically linked the ripe red fruits of an opuntia to human hearts; just as the fruit quenches thirst, so offering human hearts to the sun god ensured the sun would keep moving. Europeans first encountered cacti when they arrived in the New World late in the 15th century. Their first landfalls were in the West Indies, where relatively few cactus genera are found; one of the most common is the genus ''
Melocactus ''Melocactus'' (melon cactus), also known as the Turk's cap cactus, is a genus of cactus with about 30–40 species. They are native to the Caribbean, western Mexico through Central America to northern South America, with some species along th ...
''. Thus, melocacti were possibly among the first cacti seen by Europeans. ''Melocactus'' species were present in English collections of cacti before the end of the 16th century (by 1570 according to one source,) where they were called ''Echinomelocactus'', later shortened to ''Melocactus'' by Joseph Pitton de Tourneville in the early 18th century. Cacti, both purely ornamental species and those with edible fruit, continued to arrive in Europe, so Carl Linnaeus was able to name 22 species by 1753. One of these, his ''Cactus opuntia'' (now part of ''Opuntia ficus-indica''), was described as "" (with larger fruit ... now in Spain and Portugal), indicative of its early use in Europe.


Food

The plant now known as ''
Opuntia ficus-indica ''Opuntia ficus-indica'', the Indian fig opuntia, fig opuntia, or prickly pear, is a species of cactus that has long been a domesticated crop plant grown in agricultural economies throughout arid and semiarid parts of the world. ''O. ficus-indic ...
'', or the Indian fig cactus, has long been an important source of food. The original species is thought to have come from central Mexico, although this is now obscure because the indigenous people of southern North America developed and distributed a range of horticultural varieties ( cultivars), including forms of the species and hybrids with other opuntias. Both the fruit and pads are eaten, the former often under the Spanish name ''tuna'', the latter under the name ''
nopal Nopal (from the Nahuatl word for the pads of the plant) is a common name in Spanish for ''Opuntia'' cacti (commonly referred to in English as ''prickly pear''), as well as for its pads. There are about 114 known species in Mexico, where it ...
''. Cultivated forms are often significantly less spiny or even spineless. The nopal industry in Mexico was said to be worth US$150 million in 2007. The Indian fig cactus was probably already present in the Caribbean when the Spanish arrived, and was soon after brought to Europe. It spread rapidly in the Mediterranean area, both naturally and by being introduced—so much so, early botanists assumed it was native to the area. Outside the Americas, the Indian fig cactus is an important commercial crop in Sicily,
Algeria ) , image_map = Algeria (centered orthographic projection).svg , map_caption = , image_map2 = , capital = Algiers , coordinates = , largest_city = capital , relig ...
and other North African countries. Fruits of other opuntias are also eaten, generally under the same name, ''tuna''. Flower buds, particularly of ''
Cylindropuntia ''Cylindropuntia'' is a genus of cacti (family Cactaceae), containing species commonly known as chollas, native to northern Mexico and the Southwestern United States. They are known for their barbed spines that tenaciously attach to skin, fur, a ...
'' species, are also consumed. Almost any fleshy cactus fruit is edible. The word ''
pitaya A pitaya () or pitahaya () is the fruit of several different cactus species indigenous to the Americas. Pitaya usually refers to fruit of the genus '' Stenocereus'', while pitahaya or dragon fruit refers to fruit of the genus '' Selenicereus' ...
'' or ''pitahaya'' (usually considered to have been taken into Spanish from Haitian creole) can be applied to a range of "scaly fruit", particularly those of columnar cacti. The fruit of the
saguaro The saguaro (, ) (''Carnegiea gigantea'') is a tree-like cactus species in the monotypic genus ''Carnegiea'' that can grow to be over tall. It is native to the Sonoran Desert in Arizona, the Mexican state of Sonora, and the Whipple Mountains ...
(''Carnegiea gigantea'') has long been important to the indigenous peoples of northwestern Mexico and the southwestern United States, including the
Sonoran Desert The Sonoran Desert ( es, Desierto de Sonora) is a desert in North America and ecoregion that covers the northwestern Mexican states of Sonora, Baja California, and Baja California Sur, as well as part of the southwestern United States (in Arizona ...
. It can be preserved by boiling to produce syrup and by drying. The syrup can also be fermented to produce an alcoholic drink. Fruits of ''Stenocereus'' species have also been important food sources in similar parts of North America; '' Stenocereus queretaroensis'' is cultivated for its fruit. In more tropical southern areas, the climber ''
Selenicereus undatus ''Selenicereus undatus'', the white-fleshed pitahaya, is a species of the genus ''Selenicereus'' (formerly ''Hylocereus'') in the family Cactaceae and is the most cultivated species in the genus. It is used both as an ornamental vine and as a f ...
'' provides ''pitahaya orejona'', now widely grown in Asia under the name dragon fruit. Other cacti providing edible fruit include species of ''
Echinocereus ''Echinocereus'' is a genus of ribbed, usually small to medium-sized, cylindrical shaped cacti, comprising about 70 species native to the southern United States and Mexico in very sunny, rocky places. Usually the flowers are large and the fruit ...
'', ''
Ferocactus ''Ferocactus'' is a genus of large barrel-shaped cacti, mostly with large spines and small flowers. There are about 30 species included in the genus. They are found in the southwestern United States and northwestern Mexico. Description The y ...
'', ''
Mammillaria ''Mammillaria'' is one of the largest genera in the cactus family (Cactaceae), with currently 200 known species and varieties recognized. Most of the mammillaria are native to Mexico, but some come from the southwest United States, the Caribb ...
'', ''
Myrtillocactus ''Myrtillocactus'' (from Latin, "blueberry cactus") is a genus of cacti. The genus is found from Mexico to Guatemala. The genus is best known with '' Myrtillocactus geometrizans''. The genus ''Myrtillocereus'' Fric & Kreuz. (orth. var.) has be ...
'', ''
Pachycereus ''Pachycereus'' is a genus of 9–12 species of large cacti native to Mexico and just into southern Arizona, United States. They form large shrubs or small trees up to 15 m tall, with stout stems up to 1 m in diameter. ''Pachycereus'' comes fro ...
'', ''
Peniocereus ''Peniocereus'' is a genus of vining cacti, comprising about 18 species, found from the southwestern United States and Mexico. They have a large underground tuber, thin and inconspicuous stems. Its name comes from the prefix ''penio-'' (from the ...
'' and ''
Selenicereus ''Selenicereus'', sometimes known as moonlight cactus, is a genus of epiphytic, lithophytic, and terrestrial cacti, found in Mexico, Central America, the Caribbean and northern South America. The term night-blooming cereus is also sometimes use ...
''. The bodies of cacti other than opuntias are less often eaten, although Anderson reported that ''
Neowerdermannia vorwerkii ''Neowerdermannia vorwerkii'', also known as ''achakana'' (Aymara and Quechua), is a species of cactus from high altitudes in Bolivia and northern Argentina Argentina (), officially the Argentine Republic ( es, link=no, República Argent ...
'' is prepared and eaten like potatoes in upland Bolivia. Saguaro gatherers2.jpg, Gathering
saguaro The saguaro (, ) (''Carnegiea gigantea'') is a tree-like cactus species in the monotypic genus ''Carnegiea'' that can grow to be over tall. It is native to the Sonoran Desert in Arizona, the Mexican state of Sonora, and the Whipple Mountains ...
fruit in 1907 Saguaro fruit.jpg, Edible fruit of the saguaro Barrel Cactus Fruit cropped.jpg, Fruits of some ''
Ferocactus ''Ferocactus'' is a genus of large barrel-shaped cacti, mostly with large spines and small flowers. There are about 30 species included in the genus. They are found in the southwestern United States and northwestern Mexico. Description The y ...
'' are edible. Dragonfruit Chiayi market.jpg, Dragon fruit for sale in Taiwan Fruto de Stenocereus queretaroensis.jpg, Fruit prepared from '' Stenocereus queretaroensis'' Nopal11.jpg, Salad including sliced ''nopales'' ( opuntia pads)


Psychoactive agents

A number of species of cacti have been shown to contain psychoactive agents, chemical compounds that can cause changes in mood, perception and cognition through their effects on the brain. Two species have a long history of use by the indigenous peoples of the Americas: peyote, '' Lophophora williamsii'', in North America, and the San Pedro cactus, ''
Echinopsis pachanoi ''Echinopsis pachanoi'' (syn. ''Trichocereus pachanoi'')—known as San Pedro cactus—is a fast-growing columnar cactus native to the Andes Mountains at in altitude. It is found in Argentina, Bolivia, Colombia, Chile, Ecuador and Peru, and it ...
'', in South America. Both contain mescaline. ''L. williamsii'' is native to northern Mexico and southern Texas. Individual stems are about high with a diameter of , and may be found in clumps up to wide. A large part of the stem is usually below ground. Mescaline is concentrated in the photosynthetic portion of the stem above ground. The center of the stem, which contains the growing point (the apical meristem), is sunken. Experienced collectors of peyote remove a thin slice from the top of the plant, leaving the growing point intact, thus allowing the plant to regenerate. Evidence indicates peyote was in use more than 5,500 years ago; dried peyote buttons presumed to be from a site on the Rio Grande, Texas, were radiocarbon dated to around 3780–3660 BC. Peyote is perceived as a means of accessing the spirit world. Attempts by the Roman Catholic church to suppress its use after the Spanish conquest were largely unsuccessful, and by the middle of the 20th century, peyote was more widely used than ever by indigenous peoples as far north as Canada. It is now used formally by the
Native American Church The Native American Church (NAC), also known as Peyotism and Peyote Religion, is a Native American religion that teaches a combination of traditional Native American beliefs and Christianity, with sacramental use of the entheogen peyote. Th ...
. ''Echinopsis pachanoi'' is native to Ecuador and Peru. It is very different in appearance from ''L. williamsii''. It has tall stems, up to high, with a diameter of , which branch from the base, giving the whole plant a shrubby or tree-like appearance. Archaeological evidence of the use of this cactus appears to date back to 2,000–2,300 years ago, with carvings and ceramic objects showing columnar cacti. Although church authorities under the Spanish attempted to suppress its use, this failed, as shown by the Christian element in the common name "San Pedro cactus"—
Saint Peter ) (Simeon, Simon) , birth_date = , birth_place = Bethsaida, Gaulanitis, Syria, Roman Empire , death_date = Between AD 64–68 , death_place = probably Vatican Hill, Rome, Italia, Roman Empire , parents = John (or Jonah; Jona) , occupation ...
cactus. Anderson attributes the name to the belief that just as St Peter holds the keys to heaven, the effects of the cactus allow users "to reach heaven while still on earth." It continues to be used for its psychoactive effects, both for spiritual and for healing purposes, often combined with other psychoactive agents, such as '' Datura ferox'' and tobacco. Several other species of ''Echinopsis'', including ''E. peruviana'', also contain mescaline.


Ornamental plants

Cacti were cultivated as ornamental plants from the time they were first brought from the New World. By the early 1800s, enthusiasts in Europe had large collections (often including other succulents alongside cacti). Rare plants were sold for very high prices. Suppliers of cacti and other succulents employed collectors to obtain plants from the wild, in addition to growing their own. In the late 1800s, collectors turned to orchids, and cacti became less popular, although never disappearing from cultivation. Cacti are often grown in greenhouses, particularly in regions unsuited to the cultivation of cacti outdoors, such the northern parts of Europe and North America. Here, they may be kept in pots or grown in the ground. Cacti are also grown as houseplants, many being tolerant of the often dry atmosphere. Cacti in pots may be placed outside in the summer to ornament gardens or patios, and then kept under cover during the winter. Less drought-resistant
epiphyte An epiphyte is an organism that grows on the surface of a plant and derives its moisture and nutrients from the air, rain, water (in marine environments) or from debris accumulating around it. The plants on which epiphytes grow are called phoroph ...
s, such as
epiphyllum hybrid Epiphyllum hybrids, epiphyllums, epicacti, or just epis, also known as orchid cacti, which are widely grown for their flowers, are artificial hybrids of species within the group of cacti placed in the tribe Hylocereeae. In spite of the common na ...
s, ''
Schlumbergera ''Schlumbergera'' is a small genus of cacti with six to nine species found in the coastal mountains of south-eastern Brazil. These plants grow on trees or rocks in habitats that are generally shady with high humidity, and can be quite differen ...
'' (the Thanksgiving or Christmas cactus) and ''
Hatiora ''Hatiora'' is a small genus of epiphytic cacti which belongs to the tribe Rhipsalideae within the subfamily Cactoideae of the Cactaceae. Recent taxonomic studies have led to the three species formerly placed in subgenus ''Rhipsalidopsis'' being ...
'' (the Easter cactus), are widely cultivated as houseplants. Cacti may also be planted outdoors in regions with suitable climates. Concern for water conservation in arid regions has led to the promotion of gardens requiring less watering ( xeriscaping). For example, in California, the East Bay Municipal Utility District sponsored the publication of a book on plants and landscapes for summer-dry climates. Cacti are one group of drought-resistant plants recommended for dry landscape gardening.


Other uses

Cacti have many other uses. They are used for human food and as fodder for animals, usually after burning off their spines. In addition to their use as psychoactive agents, some cacti are employed in herbal medicine. The practice of using various species of ''Opuntia'' in this way has spread from the Americas, where they naturally occur, to other regions where they grow, such as India.
Cochineal The cochineal ( , ; ''Dactylopius coccus'') is a scale insect in the suborder Sternorrhyncha, from which the natural dye carmine is derived. A primarily sessile parasite native to tropical and subtropical South America through North America ...
is a red dye produced by a
scale insect Scale insects are small insects of the order Hemiptera, suborder Sternorrhyncha. Of dramatically variable appearance and extreme sexual dimorphism, they comprise the infraorder Coccomorpha which is considered a more convenient grouping than the ...
that lives on species of ''Opuntia''. Long used by the peoples of Central and North America, demand fell rapidly when European manufacturers began to produce synthetic dyes in the middle of the 19th century. Commercial production has now increased following a rise in demand for natural dyes. Cacti are used as construction materials. Living cactus fences are employed as barricades around buildings to prevent people breaking in. They also used to
corral A pen is an enclosure for holding livestock. It may also perhaps be used as a term for an enclosure for other animals such as pets that are unwanted inside the house. The term describes types of enclosures that may confine one or many anima ...
animals. The woody parts of cacti, such as ''
Cereus repandus ''Cereus repandus'' (syn. ''Cereus peruvianus''), the Peruvian apple cactus, is a large, erect, thorny columnar cactus found in South America. It is also known as giant club cactus, hedge cactus, ''cadushi'' (in Papiamento and WayuunaikiVillalo ...
'' and ''
Echinopsis atacamensis ''Echinopsis atacamensis'' (cardón) is a species of cactus from Chile, Argentina and Bolivia. The wood of this species can be used in building and in making furniture., pp. 257–258 Description ''Echinopsis atacamensis'' has a tall columnar ...
'', are used in buildings and in furniture. The frames of
wattle and daub Wattle and daub is a composite building method used for making walls and buildings, in which a woven lattice of wooden strips called wattle is daubed with a sticky material usually made of some combination of wet soil, clay, sand, animal dung ...
houses built by the
Seri people The Seri or ''Comcaac'' are an indigenous group of the Mexican state of Sonora. The majority reside on the Seri communal property ( es, ejido), in the towns of Punta Chueca ( sei, Socaaix) and El Desemboque ( sei, Haxöl Iihom, link=no) on t ...
of Mexico may use parts of the
saguaro The saguaro (, ) (''Carnegiea gigantea'') is a tree-like cactus species in the monotypic genus ''Carnegiea'' that can grow to be over tall. It is native to the Sonoran Desert in Arizona, the Mexican state of Sonora, and the Whipple Mountains ...
(''Carnegiea gigantea''). The very fine spines and hairs (trichomes) of some cacti were used as a source of fiber for filling pillows and in weaving.


Conservation

All cacti are included in Appendix II of the
Convention on International Trade in Endangered Species of Wild Fauna and Flora CITES (shorter name for the Convention on International Trade in Endangered Species of Wild Fauna and Flora, also known as the Washington Convention) is a multilateral treaty to protect endangered plants and animals from the threats of interna ...
(CITES), which "lists species that are not necessarily now threatened with extinction but that may become so unless trade is closely controlled." Control is exercised by making international trade in most specimens of cacti illegal unless permits have been issued, at least for exports. Some exceptions are allowed, e.g., for "naturalized or artificially propagated plants".; see "Cactaceae" and linked footnotes Some cacti, such as all ''
Ariocarpus ''Ariocarpus'' is a small genus of succulent, subtropical plants of the family Cactaceae. The name comes from the ancient Greek "aria" (an oak type) and "carpos" (=fruit) because of the resemblance of the fruit of the two genus in acorn for ...
'' and ''
Discocactus ''Discocactus'' is a genus of tropical cacti. The name comes from the ancient Greek ' (=disc) because of its shape. ''Discocactus'' plants are endemic to southern Brazil, eastern Bolivia, and northern Paraguay. These species are in the risk of ...
'' species, are included in the more restrictive Appendix I, used for the "most endangered" species. These may only be moved between countries for non-commercial purposes, and only then when accompanied by both export and import permits. The three main threats to cacti in the wild are development, grazing and over-collection. Development takes many forms. The construction of a dam near Zimapan, Mexico, caused the destruction of a large part of the natural habitat of ''
Echinocactus grusonii ''Echinocactus grusonii'' or ''Kroenleinia grusonii'', popularly known as the golden barrel cactus, golden ball or mother-in-law's cushion, is a species of barrel cactus which is endemic to east-central Mexico. It is rare and endangered in th ...
''. Urban development and highways have destroyed cactus habitats in parts of Mexico, New Mexico and Arizona, including the
Sonoran Desert The Sonoran Desert ( es, Desierto de Sonora) is a desert in North America and ecoregion that covers the northwestern Mexican states of Sonora, Baja California, and Baja California Sur, as well as part of the southwestern United States (in Arizona ...
. The conversion of land to agriculture has affected populations of ''
Ariocarpus kotschoubeyanus ''Ariocarpus kotschoubeyanus'' is a species of plant in the family Cactaceae. It is endemic to Coahuila and Nuevo León states, and southwards into Querétaro state, in northeastern Mexico. Its natural habitat is hot deserts. It was named aft ...
'' in Mexico, where dry plains were plowed for maize cultivation, and of ''
Copiapoa ''Copiapoa'' is a genus of flowering plants in the cactus family Cactaceae, from the dry coastal deserts, particularly the Atacama Desert, of northern Chile. Description It comprises 32 morphologically defined species and 5 heterotypic subspec ...
'' and ''
Eulychnia ''Eulychnia'' is a genus of candelabriform or arborescent cactus, cacti, comprising between 6 and 9 species depending on the authority. These desert cacti can survive under very hot conditions—temperatures can reach up to 50 degrees Celsius. F ...
'' in
Chile Chile, officially the Republic of Chile, is a country in the western part of South America. It is the southernmost country in the world, and the closest to Antarctica, occupying a long and narrow strip of land between the Andes to the east a ...
, where valley slopes were planted with vines. Grazing, in many areas by introduced animals, such as goats, has caused serious damage to populations of cacti (as well as other plants); two examples cited by Anderson are the
Galápagos Islands The Galápagos Islands ( Spanish: , , ) are an archipelago of volcanic islands. They are distributed on each side of the equator in the Pacific Ocean, surrounding the centre of the Western Hemisphere, and are part of the Republic of Ecuador ...
generally and the effect on '' Browningia candelaris'' in Peru. Over-collection of cacti for sale has greatly affected some species. For example, the type locality of '' Pelecyphora strobiliformis'' near
Miquihuana ''Miquihuana'' is a genus of ground beetles in the family Carabidae Ground beetles are a large, cosmopolitan family of beetles, the Carabidae, with more than 40,000 species worldwide, around 2,000 of which are found in North America and 2,700 ...
, Mexico, was virtually denuded of plants, which were dug up for sale in Europe. Illegal collecting of cacti from the wild continues to pose a threat. Conservation of cacti can be ''in situ'' or ''ex situ''. ''In situ'' conservation involves preserving habits through enforcement of legal protection and the creation of specially protected areas such as national parks and reserves. Examples of such protected areas in the United States include
Big Bend National Park Big Bend National Park is an American national park located in West Texas, bordering Mexico. The park has national significance as the largest protected area of Chihuahuan Desert topography and ecology in the United States, and was named after ...
, Texas; Joshua Tree National Park, California; and
Saguaro National Park Saguaro National Park is an American national park in Pima County, southeastern Arizona. The park consists of two separate areas—the Tucson Mountain District (TMD) about west of the city of Tucson and the Rincon Mountain District (RMD) about ...
, Arizona. Latin American examples include Parque Nacional del Pinacate, Sonora, Mexico and Pan de Azúcar National Park, Chile. ''Ex situ'' conservation aims to preserve plants and seeds outside their natural habitats, often with the intention of later reintroduction. Botanical gardens play an important role in ''ex situ'' conservation; for example, seeds of cacti and other succulents are kept in long-term storage at the
Desert Botanical Garden Desert Botanical Garden is a botanical garden located in Papago Park, at 1201 N. Galvin Parkway in Phoenix, central Arizona. Founded by the Arizona Cactus and Native Flora Society in 1937 and established at this site in 1939, the garden now ha ...
, Arizona.


Cultivation

The popularity of cacti means many books are devoted to their cultivation. Cacti naturally occur in a wide range of habitats and are then grown in many countries with different climates, so precisely replicating the conditions in which a species normally grows is usually not practical. A broad distinction can be made between semidesert cacti and epiphytic cacti, which need different conditions and are best grown separately. This section is primarily concerned with the cultivation of semidesert cacti in containers and under protection, such as in a greenhouse or in the home, rather than cultivation outside in the ground in those climates that permit it. For the cultivation of epiphytic cacti, see Cultivation of ''Schlumbergera'' (Christmas or Thanksgiving cacti), and Cultivation of epiphyllum hybrids.


Growing medium

The purpose of the growing medium is to provide support and to store water, oxygen and dissolved minerals to feed the plant. In the case of cacti, there is general agreement that an open medium with a high air content is important. When cacti are grown in containers, recommendations as to how this should be achieved vary greatly; Miles Anderson says that if asked to describe a perfect growing medium, "ten growers would give 20 different answers". Roger Brown suggests a mixture of two parts commercial soilless growing medium, one part hydroponic clay and one part coarse pumice or perlite, with the addition of soil from earthworm castings. The general recommendation of 25–75% organic-based material, the rest being inorganic such as pumice, perlite or grit, is supported by other sources. However, the use of organic material is rejected altogether by others; Hecht says that cacti (other than epiphytes) "want soil that is low in or free of
humus In classical soil science, humus is the dark organic matter in soil that is formed by the decomposition of plant and animal matter. It is a kind of soil organic matter. It is rich in nutrients and retains moisture in the soil. Humus is the Latin ...
", and recommends coarse sand as the basis of a growing medium.


Watering

Semi-desert cacti need careful watering. General advice is hard to give, since the frequency of watering required depends on where the cacti are being grown, the nature of the growing medium, and the original habitat of the cacti. Brown says that more cacti are lost through the "untimely application of water than for any other reason" and that even during the dormant winter season, cacti need some water. Other sources say that water can be withheld during winter (November to March in the Northern Hemisphere). Another issue is the hardness of the water; where it is necessary to use hard water, regular re-potting is recommended to avoid the build up of salts. The general advice given is that during the growing season, cacti should be allowed to dry out between thorough waterings. A water meter can help in determining when the soil is dry.


Light and temperature

Although semi-desert cacti may be exposed to high light levels in the wild, they may still need some shading when subjected to the higher light levels and temperatures of a greenhouse in summer. Allowing the temperature to rise above is not recommended. The minimum winter temperature required depends very much on the species of cactus involved. For a mixed collection, a minimum temperature of between and is often suggested, except for cold-sensitive genera such as ''
Melocactus ''Melocactus'' (melon cactus), also known as the Turk's cap cactus, is a genus of cactus with about 30–40 species. They are native to the Caribbean, western Mexico through Central America to northern South America, with some species along th ...
'' and ''
Discocactus ''Discocactus'' is a genus of tropical cacti. The name comes from the ancient Greek ' (=disc) because of its shape. ''Discocactus'' plants are endemic to southern Brazil, eastern Bolivia, and northern Paraguay. These species are in the risk of ...
''. Some cacti, particularly those from the high Andes, are fully frost-hardy when kept dry (e.g. ''
Rebutia minuscula ''Rebutia minuscula'' is a species of cactus from South America found in northern Argentina and Bolivia., p. 605 It is the type species of the genus ''Rebutia''. As its synonym ''Rebutia senilis'' it has gained the Royal Horticultural Society’s ...
'' survives temperatures down to in cultivation) and may flower better when exposed to a period of cold.


Propagation

Cacti can be propagated by seed, cuttings or grafting. Seed sown early in the year produces seedlings that benefit from a longer growing period. Seed is sown in a moist growing medium and then kept in a covered environment, until 7–10 days after germination, to avoid drying out. A very wet growing medium can cause both seeds and seedlings to rot. A temperature range of is suggested for germination; soil temperatures of around promote the best root growth. Low light levels are sufficient during germination, but afterwards semi-desert cacti need higher light levels to produce strong growth, although
acclimatization Acclimatization or acclimatisation ( also called acclimation or acclimatation) is the process in which an individual organism adjusts to a change in its environment (such as a change in altitude, temperature, humidity, photoperiod, or pH), a ...
is needed to conditions in a greenhouse, such as higher temperatures and strong sunlight. Reproduction by cuttings makes use of parts of a plant that can grow roots. Some cacti produce "pads" or "joints" that can be detached or cleanly cut off. Other cacti produce offsets that can be removed. Otherwise, stem cuttings can be made, ideally from relatively new growth. It is recommended that any cut surfaces be allowed to dry for a period of several days to several weeks until a
callus A callus is an area of thickened and sometimes hardened skin that forms as a response to repeated friction, pressure, or other irritation. Since repeated contact is required, calluses are most often found on the feet and hands, but they may o ...
forms over the cut surface. Rooting can then take place in an appropriate growing medium at a temperature of around . Grafting is used for species difficult to grow well in cultivation or that cannot grow independently, such as some
chlorophyll Chlorophyll (also chlorophyl) is any of several related green pigments found in cyanobacteria and in the chloroplasts of algae and plants. Its name is derived from the Greek words , ("pale green") and , ("leaf"). Chlorophyll allow plants to ...
-free forms with white, yellow or red bodies, or some forms that show abnormal growth (e.g., cristate or forms). For the host plant (the stock), growers choose one that grows strongly in cultivation and is compatible with the plant to be propagated: the
scion Scion may refer to: Arts, entertainment, and media Fictional entities *Scion, a playable class in the game ''Path of Exile'' (2013) *Atlantean Scion, a device in the ''Tomb Raider'' video game series *Scions, an alien race in the video game '' B ...
. The grower makes cuts on both stock and scion and joins the two, binding them together while they unite. Various kinds of graft are used—flat grafts, where both scion and stock are of similar diameters, and cleft grafts, where a smaller scion is inserted into a cleft made in the stock. Commercially, huge numbers of cacti are produced annually. For example, in 2002 in Korea alone, 49 million plants were propagated, with a value of almost US$9 million. Most of them (31 million plants) were propagated by grafting.


Pests and diseases

A range of pests attack cacti in cultivation. Those that feed on sap include
mealybug Mealybugs are insects in the family Pseudococcidae, unarmored scale insects found in moist, warm habitats. Many species are considered pests as they feed on plant juices of greenhouse plants, house plants and subtropical trees and also act as a ...
s, living on both stems and roots;
scale insect Scale insects are small insects of the order Hemiptera, suborder Sternorrhyncha. Of dramatically variable appearance and extreme sexual dimorphism, they comprise the infraorder Coccomorpha which is considered a more convenient grouping than the ...
s, generally only found on stems; whiteflies, which are said to be an "infrequent" pest of cacti; red spider mites, which are very small but can occur in large numbers, constructing a fine web around themselves and badly marking the cactus via their sap sucking, even if they do not kill it; and thrips, which particularly attack flowers. Some of these pests are resistant to many insecticides, although there are
biological control Biological control or biocontrol is a method of controlling pests, such as insects, mites, weeds, and plant diseases, using other organisms. It relies on predation, parasitism, herbivory, or other natural mechanisms, but typically also invo ...
s available. Roots of cacti can be eaten by the larvae of sciarid flies and fungus gnats.
Slug Slug, or land slug, is a common name for any apparently shell-less terrestrial gastropod mollusc. The word ''slug'' is also often used as part of the common name of any gastropod mollusc that has no shell, a very reduced shell, or only a smal ...
s and snails also eat cacti. Fungi, bacteria and viruses attack cacti, the first two particularly when plants are over-watered. Fusarium rot can gain entry through a wound and cause rotting accompanied by red-violet mold. "''Helminosporium'' rot" is caused by '' Bipolaris cactivora'' ( ''Helminosporium cactivorum''); ''Phytophthora'' species also cause similar rotting in cacti. Fungicides may be of limited value in combating these diseases. Several viruses have been found in cacti, including cactus virus X. These appear to cause only limited visible symptoms, such as
chlorotic In botany, chlorosis is a condition in which leaves produce insufficient chlorophyll. As chlorophyll is responsible for the green color of leaves, chlorotic leaves are pale, yellow, or yellow-white. The affected plant has little or no ability to ...
(pale green) spots and mosaic effects (streaks and patches of paler color). However, in an ''Agave'' species, cactus virus X has been shown to reduce growth, particularly when the roots are dry. There are no treatments for virus diseases.


Notes


References


Bibliography

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External links

* * * * {{Authority control Drought-tolerant plants Eocene plants Priabonian first appearances Extant Eocene first appearances Taxa named by Carl Linnaeus Western (genre) staples and terminology