A cactus (: cacti, cactuses, or less commonly, cactus) is a member of the

plant Plants are the eukaryotes that form the Kingdom (biology), kingdom Plantae; they are predominantly Photosynthesis, photosynthetic. This means that they obtain their energy from sunlight, using chloroplasts derived from endosymbiosis with c ...

family Cactaceae (), a family of the order

Caryophyllales Caryophyllales ( ) is a diverse and heterogeneous order of flowering plants with well-known members including cacti, carnations, beets, quinoa, spinach, amaranths, pigfaces and ice plants, oraches and saltbushes, goosefoots, sundews, Venu ...

comprising about 127 genera with some 1,750 known species. The word ''cactus'' derives, through Latin, from the

Ancient Greek Ancient Greek (, ; ) includes the forms of the Greek language used in ancient Greece and the classical antiquity, ancient world from around 1500 BC to 300 BC. It is often roughly divided into the following periods: Mycenaean Greek (), Greek ...

word (''káktos''), a name originally used by

Theophrastus Theophrastus (; ; c. 371 – c. 287 BC) was an ancient Greek Philosophy, philosopher and Natural history, naturalist. A native of Eresos in Lesbos, he was Aristotle's close colleague and successor as head of the Lyceum (classical), Lyceum, the ...

for a spiny plant whose identity is now not certain. Cacti occur in a wide range of shapes and sizes. They are native to the Americas, ranging from

Patagonia Patagonia () is a geographical region that includes parts of Argentina and Chile at the southern end of South America. The region includes the southern section of the Andes mountain chain with lakes, fjords, temperate rainforests, and glaciers ...

in the south to parts of western

Canada Canada is a country in North America. Its Provinces and territories of Canada, ten provinces and three territories extend from the Atlantic Ocean to the Pacific Ocean and northward into the Arctic Ocean, making it the world's List of coun ...

in the north, with the exception of '' Rhipsalis baccifera'', which is also found in

Africa Africa is the world's second-largest and second-most populous continent after Asia. At about 30.3 million km2 (11.7 million square miles) including adjacent islands, it covers 20% of Earth's land area and 6% of its total surfac ...

and

Sri Lanka Sri Lanka, officially the Democratic Socialist Republic of Sri Lanka, also known historically as Ceylon, is an island country in South Asia. It lies in the Indian Ocean, southwest of the Bay of Bengal, separated from the Indian subcontinent, ...

. Cacti are adapted to live in very dry environments, including the

Atacama Desert The Atacama Desert () is a desert plateau located on the Pacific Ocean, Pacific coast of South America, in the north of Chile. Stretching over a strip of land west of the Andes Mountains, it covers an area of , which increases to if the barre ...

, one of the driest places on Earth. Because of this, cacti show many adaptations to conserve water. For example, almost all cacti are

succulent 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 ...

s, 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 evolved to feed on plants, especially upon vascular tissues such as foliage, fruits or seeds, as the main component of its diet. These more broadly also encompass animals that eat ...

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 Photosynthesis ( ) is a system of biological processes by which photosynthetic organisms, such as most plants, algae, and cyanobacteria, convert light energy, typically from sunlight, into the chemical energy necessary to fuel their metabo ...

. Cactus spines are produced from specialized structures called

areole In botany, areoles are small light- to dark-colored bumps on cactus, cacti out of which grow clusters of Thorns, spines, and prickles, spines. Areoles are important diagnostic features of cactus, cacti, and identify them as a family distinct fr ...

s, a kind of highly reduced branch. Areoles are an identifying feature of cacti. As well as spines, areoles give rise to

flower Flowers, also known as blooms and blossoms, are the reproductive structures of flowering plants ( angiosperms). Typically, they are structured in four circular levels, called whorls, around the end of a stalk. These whorls include: calyx, m ...

s, which are usually tubular and multipetaled. Many cacti have short

growing season A season is a division of the year marked by changes in weather, ecology, and the amount of daylight. The growing season is that portion of the year in which local conditions (i.e. rainfall, temperature, daylight) permit normal plant growth. Whi ...

s 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 with a number of ribs which corresponds to a number in the

Fibonacci numbers In mathematics, the Fibonacci sequence is a sequence in which each element is the sum of the two elements that precede it. Numbers that are part of the Fibonacci sequence are known as Fibonacci numbers, commonly denoted . Many writers begin the s ...

(2, 3, 5, 8, 13, 21, 34 etc.). This allows them to expand and contract easily for quick water absorption after rain, followed by retention over long

drought A drought is a period of drier-than-normal conditions.Douville, H., K. Raghavan, J. Renwick, R.P. Allan, P.A. Arias, M. Barlow, R. Cerezo-Mota, A. Cherchi, T.Y. Gan, J. Gergis, D. Jiang, A. Khan, W. Pokam Mba, D. Rosenfeld, J. Tierney, ...

periods. Like other succulent plants, most cacti employ a special mechanism called " crassulacean acid metabolism" (CAM) as part of photosynthesis.

Transpiration Transpiration is the process of water movement through a plant and its evaporation from aerial parts, such as leaves, stems and flowers. It is a passive process that requires no energy expense by the plant. Transpiration also cools plants, c ...

, during which

carbon dioxide Carbon dioxide is a chemical compound with the chemical formula . It is made up of molecules that each have one carbon atom covalent bond, covalently double bonded to two oxygen atoms. It is found in a gas state at room temperature and at norma ...

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 Malic acid is an organic compound with the molecular formula . It is a dicarboxylic acid that is made by all living organisms, contributes to the sour taste of fruits, and is used as a food additive. Malic acid has two stereoisomeric forms ( ...

, 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 Transpiration is the process of water movement through a plant and its evaporation from aerial parts, such as leaves, stems and flowers. It is a passive process that requires no energy expense by the plant. Transpiration also cools plants, c ...

. 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'') 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'', '' Rhodocactus'' and '' Pereskia'' 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 Water conservation aims to sustainably manage the natural resource of fresh water, protect the hydrosphere, and meet current and future human demand. Water conservation makes it possible to avoid water scarcity. It covers all the policies, strateg ...

. ''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 a plant or plant-like organism that grows on the surface of another 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 epiphyt ...

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 cactus, 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 d ...

''). 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 sessility (motility), sessile parasitism, parasite native to tropical and subtropical Sout ...

is the product of an insect that lives on some cacti. Many

succulent plant 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'', meanin ...

s in both the Old and

New World The term "New World" is used to describe the majority of lands of Earth's Western Hemisphere, particularly the Americas, and sometimes Oceania."America." ''The Oxford Companion to the English Language'' (). McArthur, Tom, ed., 1992. New York: ...

– such as some

Euphorbiaceae Euphorbiaceae (), the spurge family, is a large family of flowering plants. In English, they are also commonly called euphorbias, which is also the name of Euphorbia, the type genus of the family. Most spurges, such as ''Euphorbia paralias'', ar ...

(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, and are widely distributed throughout the Americas. Cactaceae is the 5th most endangered plant or animal family evaluated globally by the International Union for Conservati ...

). Most members of these two groups are easily recognizable as cacti. They have fleshy

stems that are major organs of

. They have absent, small, or transient

leaves A leaf (: leaves) is a principal appendage of the stem of a vascular plant, usually borne laterally above ground and specialized for photosynthesis. Leaves are collectively called foliage, as in "autumn foliage", while the leaves, stem, ...

. They have

flowers Flowers, also known as blooms and blossoms, are the reproductive structures of flowering plants ( angiosperms). Typically, they are structured in four circular levels, called whorls, around the end of a stalk. These whorls include: calyx, m ...

with

ovaries The ovary () is a gonad in the female reproductive system that produces ova; when released, an ovum travels through the fallopian tube/oviduct into the uterus. There is an ovary on the left and the right side of the body. The ovaries are endocr ...

that lie below the

sepals A sepal () is a part of the flower of angiosperms (flowering plants). Usually green, sepals typically function as protection for the flower in bud, and often as support for the petals when in bloom., p. 106 Etymology The term ''sepalum'' ...

and

petals Petals are modified leaves that form an inner whorl surrounding the reproductive parts of flowers. They are often brightly coloured or unusually shaped to attract pollinators. All of the petals of a flower are collectively known as the ''coroll ...

, often deeply sunken into a fleshy receptacle (the part of the stem from which the flower parts grow). All cacti have

s—highly specialized short shoots with extremely short internodes that produce spines, normal shoots, and flowers. The remaining cacti fall into only two groups: three tree-like genera, '' Leuenbergeria'', '' Pereskia'' and '' Rhodocactus'' (all formerly placed in ''Pereskia''), and the much smaller '' Maihuenia''. 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, in that when mature, they have woody stems that may be covered with

bark Bark may refer to: Common meanings * 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) Arts and entertainment * ''Bark'' (Jefferson Airplane album), ...

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. A 1903 paper in the ''American Journal of Psychology'' defined a "habit, from the standpoint of psychology, trunk topped by several to many branch">Trunk (botany)">trunk topped by several to many branches. 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

opuntia ''Opuntia'', commonly called the prickly pear cactus, is a genus of flowering plants in the cactus family Cactaceae, many known for their flavorful fruit and showy flowers. Cacti are native to the Americas, and are well adapted to arid clima ...

s. Some cacti may become tree-sized but without branches, such as larger specimens of ''Echinocactus platyacanthus''. 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 ''Stenocereus thurberi'', the organ pipe cactus, is a species of cactus native to Mexico and the United States. The species is found in rocky desert. Two subspecies are recognized based on their distribution and height. The Organ Pipe Cactus Nati ...

''. ; 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'', 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

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'' was reported as long from root to the most distant stem. Epiphytic cacti, such as species of '' Rhipsalis'' or ''

'', often hang downwards, forming dense clumps where they grow in trees high above the ground. Pereskia aculeata5.jpg, Treelike habit ('' Pereskia aculeata'') Cardon Pachycereus pringlei.jpg, Tall treelike habit ('' Pachycereus pringlei'') Cephalocereus columna-trajani rev.jpg, Tall unbranched columnar habit ('' Cephalocereus'') Ferocactus1.jpg, Shorter clustered columnar habit ('' Ferocactus pilosus'') Ferocactus echidne var victoriensis 1.jpg, Solitary globular habit ('' Ferocactus echidne'') Rebutia flavistylus 2 rev.jpg, Clustered globular habit ('' Rebutia'' species) Rhipsalis paradoxa.jpg, Epiphytic cactus ('' Rhipsalis paradoxa'') Great Variety of Cacti at the Desert Botanical Garden.jpg, There is a wide variety of cacti at the Desert Botanical Garden

Stems

The leafless, spiny stem is the characteristic feature of the majority of cacti (all belonging to the largest subfamily, the

). 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 ''Opuntia'', commonly called the prickly pear cactus, is a genus of flowering plants in the cactus family Cactaceae, many known for their flavorful fruit and showy flowers. Cacti are native to the Americas, and are well adapted to arid clima ...

'') 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 mammillarias are native to Mexico, while some come from the Southwestern United States, the C ...

'' and outgrowths almost like leaves in '' Ariocarpus'' 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 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 allows plants to absorb energy ...

and are able to carry out photosynthesis; they also have

stomata In botany, a stoma (: stomata, from Greek ''στόμα'', "mouth"), also called a stomate (: stomates), is a pore found in the epidermis of leaves, stems, and other organs, that controls the rate of gas exchange between the internal air spa ...

(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 cactus, cacti out of which grow clusters of Thorns, spines, and prickles, spines. Areoles are important diagnostic features of cactus, cacti, and identify them as a family distinct fr ...

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'', 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 (

trichome Trichomes (; ) are fine outgrowths or appendages on plants, algae, lichens, and certain protists. They are of diverse structure and function. Examples are hairs, glandular hairs, scales, and papillae. A covering of any kind of hair on a plant ...

s) 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 ''

'' and '' Neoraimondia''.

Leaves

The great majority of cacti have no visible

; 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'', '' Pereskia'' and '' Rhodocactus'' 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 Paraphyly is a taxonomic term describing a grouping that consists of the grouping's last common ancestor and some but not all of its descendant lineages. The grouping is said to be paraphyletic ''with respect to'' the excluded subgroups. In co ...

, forming two taxonomic

clade In biology, a clade (), also known as a Monophyly, monophyletic group or natural group, is a group of organisms that is composed of a common ancestor and all of its descendants. Clades are the fundamental unit of cladistics, a modern approach t ...

s. Many cacti in the opuntia group (subfamily

) also have visible leaves, which may be long-lasting (as in '' Pereskiopsis'' species) or produced only during the growing season and then lost (as in many species of ''

''). The small genus '' Maihuenia'' 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 essent ...

, and in defining

axillary bud The axillary bud (or lateral bud) is an Plant embryogenesis, embryonic or Organogenesis#Plant organogenesis, organogenic Shoot (botany), shoot located in the axil of a leaf. Each bud has the potential to form shoots, and may be specialized in prod ...

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'', '' Pereskiopsis'' and '' Maihuenia'', 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'' and ''

'', but also of some ground-living cacti, such as '' Ariocarpus''. 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 ''Mammillaria rekoi'' is a species of cactus endemic to Mexico. Distribution and habitat ''Mammillaria rekoi'' is found only in central and northern Oaxaca, Mexico. It grows in oak forests on basalt, limestone cliffs, and clay soils at altitudes ...

''). In addition to normal-length spines, members of the subfamily Opuntioideae have relatively short spines, called

glochid Glochids or glochidia (: "glochidium") are hair-like spines or short prickles, generally barbed, found on the areoles of Cactus, cacti in the sub-family ''Opuntioideae''. Cactus glochids easily detach from the plant and lodge in the skin, causi ...

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'' Hakendornen IMGP7026 WP.jpg, Hooked central spine (cf. ''

'') Toumeya papyracantha fh 087 3 AZ BB.jpg, Unusual flattened spines of '' Sclerocactus papyracanthus'' Opuntia microdasys 01 ies cropped.jpg, Glochids of '' Opuntia microdasys''

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

taproot 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 taproot ...

s; in genera such as '' Ariocarpus'', 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, produced along the stems where these come into contact with a rooting medium.

Flowers

Like their spines, cactus

s are variable. Typically, the

ovary The ovary () is a gonad in the female reproductive system that produces ova; when released, an ovum travels through the fallopian tube/ oviduct into the uterus. There is an ovary on the left and the right side of the body. The ovaries are end ...

is surrounded by material derived from stem or receptacle tissue, forming a structure called a pericarpel. Tissue derived from the

petal Petals are modified leaves that form an inner whorl surrounding the reproductive parts of flowers. They are often brightly coloured or unusually shaped to attract pollinators. All of the petals of a flower are collectively known as the ''corol ...

s and

sepal A sepal () is a part of the flower of angiosperms (flowering plants). Usually green, sepals typically function as protection for the flower in bud, and often as support for the petals when in bloom., p. 106 Etymology The term ''sepalum'' ...

s 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

s that produce wool and spines. Typically, the tube also has small scale-like

bract In botany, a bract is a modified or specialized leaf, associated with a reproductive structure such as a flower, inflorescence axis or cone scale. Bracts are usually different from foliage leaves in size, color, shape or texture. They also lo ...

s, 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 "

tepal A tepal is one of the outer parts of a flower (collectively the perianth). The term is used when these parts cannot easily be classified as either sepals or petals. This may be because the parts of the perianth are undifferentiated (i.e. of very ...

s"). Some cacti produce floral tubes without wool or spines (e.g. '' Gymnocalycium'') or completely devoid of any external structures (e.g. ''

''). Unlike the flowers of most other cacti, '' Pereskia'' flowers may be borne in clusters. Cactus flowers usually have many

stamen The stamen (: stamina or stamens) is a part consisting of the male reproductive organs of a flower. Collectively, the stamens form the androecium., p. 10 Morphology and terminology A stamen typically consists of a stalk called the filament ...

s, but only a single

style Style, or styles may refer to: Film and television * ''Style'' (2001 film), a Hindi film starring Sharman Joshi, Riya Sen, Sahil Khan and Shilpi Mudgal * ''Style'' (2002 film), a Tamil drama film * ''Style'' (2004 film), a Burmese film * '' ...

, 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 spir ...

) 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—

s and cactoids—specialize in surviving in hot and dry environments (i.e. are xerophytes), 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 have become adapted to life as climbers or

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'' (which is close to the ancestral species from which all cacti evolved) does have long-lasting leaves, which are, however, thickened and

in many species. Other species of cactus with long-lasting leaves, such as the opuntioid '' Pereskiopsis'', 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

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

. 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'') 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 Metabolism (, from ''metabolē'', "change") is the set of life-sustaining chemical reactions in organisms. The three main functions of metabolism are: the conversion of the energy in food to energy available to run cellular processes; the co ...

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'' 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

s. 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

in northern Chile.

Metabolism

Photosynthesis Photosynthesis ( ) is a system of biological processes by which photosynthetic organisms, such as most plants, algae, and cyanobacteria, convert light energy, typically from sunlight, into the chemical energy necessary to fuel their metabo ...

requires plants to take in

gas (). As they do so, they lose water through

. Like other types of succulents, 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) and then into products such as

carbohydrate A carbohydrate () is a biomolecule composed of carbon (C), hydrogen (H), and oxygen (O) atoms. The typical hydrogen-to-oxygen atomic ratio is 2:1, analogous to that of water, and is represented by the empirical formula (where ''m'' and ''n'' ...

s. The access of air to internal spaces within a plant is controlled by

stoma In botany, a stoma (: stomata, from Greek language, Greek ''στόμα'', "mouth"), also called a stomate (: stomates), is a pore found in the Epidermis (botany), epidermis of leaves, stems, and other organs, that controls the rate of gas exc ...

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 An enzyme () is a protein that acts as a biological catalyst by accelerating chemical reactions. The molecules upon which enzymes may act are called substrate (chemistry), substrates, and the enzyme converts the substrates into different mol ...

that captures starts to capture more and more oxygen instead, reducing the efficiency of photosynthesis by up to 25%. Crassulacean acid metabolism (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 cell, plant and Fungus, fungal Cell (biology), cells and some protist, animal, and bacterial cells. Vacuoles are essentially enclosed compartments which are filled with water ...

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 An isotopic signature (also isotopic fingerprint) is a ratio of non-radiogenic ' stable isotopes', stable radiogenic isotopes, or unstable radioactive isotopes of particular elements in an investigated material. The ratios of isotopes in a sample ...

—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

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" – a plant tissue made up of relatively unspecialized cells containing

chloroplast A chloroplast () is a type of membrane-bound organelle, organelle known as a plastid that conducts photosynthesis mostly in plant cell, plant and algae, algal cells. Chloroplasts have a high concentration of chlorophyll pigments which captur ...

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 Carl Linnaeus (23 May 1707 – 10 January 1778), also known after ennoblement in 1761 as Carl von Linné,#Blunt, Blunt (2004), p. 171. was a Swedish biologist and physician who formalised binomial nomenclature, the modern system of naming o ...

. In 1737, he placed the cacti he knew into two genera, ''Cactus'' and ''Pereskia''. However, when he published ''

Species Plantarum ' (Latin for "The Species of Plants") is a book by Carl Linnaeus, originally published in 1753, which lists every species of plant known at the time, classified into genus, genera. It is the first work to consistently apply binomial nomenclature ...

'' 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

(''kaktos''), a name used by

for a spiny plant, which may have been the cardoon (''Cynara cardunculus''). Later botanists, such as

Philip Miller Philip Miller Royal Society, FRS (1691 – 18 December 1771) was an English botany, botanist and gardener of Scottish descent. Miller was chief gardener at the Chelsea Physic Garden for nearly 50 years from 1722, and wrote the highly popular ...

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". 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 or ICNafp) 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 tho ...

'' (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 pu ...

, 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 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

, both the "normal" C₃ mechanism and crassulean acid metabolism (CAM)—an "advanced" feature of cacti and other succulents 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 In biological cladistics for the classification of organisms, monophyly is the condition of a taxonomic grouping being a clade – that is, a grouping of organisms which meets these criteria: # the grouping contains its own most recent co ...

, and it has been split into three genera, '' Leuenbergeria'', '' Rhodocactus'' and a narrowly circumscribed '' Pereskia''. ''Leuenbergeria'' is then placed on its own in a separate monogeneric subfamily, Leuenbergerioideae. * Subfamily

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, photosynthesis, 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 ...

s). Plants vary in size from the small cushions of '' Maihueniopsis'' to treelike species of ''Opuntia'', rising to or more. * Subfamily Maihuenioideae 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

: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 An epiphyte is a plant or plant-like organism that grows on the surface of another 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 epiphyt ...

. 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,

and Rhipsalideae, contain climbing or

forms with a rather different appearance; their stems are flattened and may be divided into segments. Molecular phylogenetic studies have supported the

monophyly In biological cladistics for the classification of organisms, monophyly is the condition of a taxonomic grouping being a clade – that is, a grouping of organisms which meets these criteria: # the grouping contains its own most recent comm ...

of three of these subfamilies, but not Pereskioideae; nor have they supported all of the tribes or even genera below this level. 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'' as then circumscribed (''Pereskia'' sensu lato) was basal within the Cactaceae, but confirmed earlier suggestions it was not

, i.e., did not include all the descendants of a common ancestor. The Bayesian consensus

cladogram A cladogram (from Greek language, Greek ''clados'' "branch" and ''gramma'' "character") is a diagram used in cladistics to show relations among organisms. A cladogram is not, however, an Phylogenetic tree, evolutionary tree because it does not s ...

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'' 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

early in the plants' life and also lack

ta—structures that control admission of air into a plant and hence control

. By contrast, caulocacti, including species of '' Rhodocactus'' 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'' 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

). 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

, 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.

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'' to parts of the

Old World The "Old World" () is a term for Afro-Eurasia coined by Europeans after 1493, when they became aware of the existence of the Americas. It is used to contrast the continents of Africa, Europe, and Asia in the Eastern Hemisphere, previously ...

, cacti are plants of

South America South America is a continent entirely in the Western Hemisphere and mostly in the Southern Hemisphere, with a considerably smaller portion in the Northern Hemisphere. It can also be described as the southern Subregion#Americas, subregion o ...

and mainly southern regions of

North America North America is a continent in the Northern Hemisphere, Northern and Western Hemisphere, Western hemispheres. North America is bordered to the north by the Arctic Ocean, to the east by the Atlantic Ocean, to the southeast by South Ameri ...

. This suggests the family must have evolved after the ancient continent of

Gondwana Gondwana ( ; ) was a large landmass, sometimes referred to as a supercontinent. The remnants of Gondwana make up around two-thirds of today's continental area, including South America, Africa, Antarctica, Australia (continent), Australia, Zea ...

split into South America and

, which occurred during the

Early Cretaceous The Early Cretaceous (geochronology, geochronological name) or the Lower Cretaceous (chronostratigraphy, chronostratigraphic name) is the earlier or lower of the two major divisions of the Cretaceous. It is usually considered to stretch from 143.1 ...

, 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 The Late Cretaceous (100.5–66 Ma) is the more recent of two epochs into which the Cretaceous Period is divided in the geologic time scale. Rock strata from this epoch form the Upper Cretaceous Series. The Cretaceous is named after ''cre ...

. More recent molecular studies suggest a much younger origin, perhaps in very Late

Eocene The Eocene ( ) is a geological epoch (geology), epoch that lasted from about 56 to 33.9 million years ago (Ma). It is the second epoch of the Paleogene Period (geology), Period in the modern Cenozoic Era (geology), Era. The name ''Eocene'' comes ...

to early

Oligocene The Oligocene ( ) is a geologic epoch (geology), epoch of the Paleogene Geologic time scale, Period that extends from about 33.9 million to 23 million years before the present ( to ). As with other older geologic periods, the rock beds that defin ...

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 The Andes ( ), Andes Mountains or Andean Mountain Range (; ) are the List of longest mountain chains on Earth, longest continental mountain range in the world, forming a continuous highland along the western edge of South America. The range ...

, 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 The Miocene ( ) is the first epoch (geology), geological epoch of the Neogene Period and extends from about (Ma). The Miocene was named by Scottish geologist Charles Lyell; the name comes from the Greek words (', "less") and (', "new") and mea ...

into the

Pliocene The Pliocene ( ; also Pleiocene) is the epoch (geology), epoch in the geologic time scale that extends from 5.33 to 2.58Aizoaceae The Aizoaceae (), or fig-marigold family, is a large family of dicotyledonous flowering plants containing 135 genera and about 1,800 species. Several genera are commonly known as 'ice plants' or 'carpet weeds'. The Aizoaceae are also referred to a ...

in South Africa, the Didiereaceae in Madagascar and the genus ''

Agave ''Agave'' (; ; ) is a genus of monocots native to the arid regions of the Americas. The genus is primarily known for its succulent and xerophytic species that typically form large Rosette (botany), rosettes of strong, fleshy leaves. Many plan ...

'' 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, sometimes collectively called America, are a landmass comprising the totality of North America and South America.''Webster's New World College Dictionary'', 2010 by Wiley Publishing, Inc., Cleveland, Ohio. When viewed as a sing ...

, where their range extends from

British Columbia British Columbia is the westernmost Provinces and territories of Canada, province of Canada. Situated in the Pacific Northwest between the Pacific Ocean and the Rocky Mountains, the province has a diverse geography, with rugged landscapes that ...

and

Alberta Alberta is a Provinces and territories of Canada, province in Canada. It is a part of Western Canada and is one of the three Canadian Prairies, prairie provinces. Alberta is bordered by British Columbia to its west, Saskatchewan to its east, t ...

in western

. A number of centers of diversity exist. For cacti adapted to drought, the three main centers are the deserts of North America; the southwestern

, where they are found in

Peru Peru, officially the Republic of Peru, is a country in western South America. It is bordered in the north by Ecuador and Colombia, in the east by Brazil, in the southeast by Bolivia, in the south by Chile, and in the south and west by the Pac ...

Bolivia Bolivia, officially the Plurinational State of Bolivia, is a landlocked country located in central South America. The country features diverse geography, including vast Amazonian plains, tropical lowlands, mountains, the Gran Chaco Province, w ...

Chile Chile, officially the Republic of Chile, is a country in western South America. It is the southernmost country in the world and the closest to Antarctica, stretching along a narrow strip of land between the Andes, Andes Mountains and the Paci ...

and

Argentina Argentina, officially the Argentine Republic, is a country in the southern half of South America. It covers an area of , making it the List of South American countries by area, second-largest country in South America after Brazil, the fourt ...

; and the

Caatinga Caatinga () is a type of semi-arid tropical vegetation, and an ecoregion characterized by this vegetation in interior northeastern Brazil. The name "Caatinga" comes from the Tupi word '' ka'atinga'', meaning "white forest" or "white vegetat ...

of eastern

Brazil Brazil, officially the Federative Republic of Brazil, is the largest country in South America. It is the world's List of countries and dependencies by area, fifth-largest country by area and the List of countries and dependencies by population ...

. 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; and in forested regions of

Central America Central America is a subregion of North America. Its political boundaries are defined as bordering Mexico to the north, Colombia to the southeast, the Caribbean to the east, and the Pacific Ocean to the southwest. Central America is usually ...

, where the climbing

are most diverse. '' Rhipsalis baccifera'' is the exception; it is native to both the Americas and the

, where it is found in tropical

Madagascar Madagascar, officially the Republic of Madagascar, is an island country that includes the island of Madagascar and numerous smaller peripheral islands. Lying off the southeastern coast of Africa, it is the world's List of islands by area, f ...

, and

. One theory is it was spread by being carried as

seed In botany, a seed is a plant structure containing an embryo and stored nutrients in a protective coat called a ''testa''. More generally, the term "seed" means anything that can be Sowing, sown, which may include seed and husk or tuber. Seeds ...

s in the

digestive tract The gastrointestinal tract (GI tract, digestive tract, alimentary canal) is the tract or passageway of the Digestion, digestive system that leads from the mouth to the anus. The tract is the largest of the body's systems, after the cardiovascula ...

s of migratory

bird Birds are a group of warm-blooded vertebrates constituting the class (biology), class Aves (), characterised by feathers, toothless beaked jaws, the Oviparity, laying of Eggshell, hard-shelled eggs, a high Metabolism, metabolic rate, a fou ...

s; the seeds of ''Rhipsalis'' are adapted for bird distribution. Old World populations are

polyploid Polyploidy is a condition in which the biological cell, cells of an organism have more than two paired sets of (Homologous chromosome, homologous) chromosomes. Most species whose cells have Cell nucleus, nuclei (eukaryotes) are diploid, meaning ...

, 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 Australia, officially the Commonwealth of Australia, is a country comprising mainland Australia, the mainland of the Australia (continent), Australian continent, the island of Tasmania and list of islands of Australia, numerous smaller isl ...

Hawaii Hawaii ( ; ) is an island U.S. state, state of the United States, in the Pacific Ocean about southwest of the U.S. mainland. One of the two Non-contiguous United States, non-contiguous U.S. states (along with Alaska), it is the only sta ...

, and the Mediterranean region. In Australia, species of ''

'', particularly '' Opuntia stricta'', 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 sessility (motility), sessile parasitism, parasite native to tropical and subtropical Sout ...

industry. They rapidly became a major weed problem, but are now controlled by biological agents, particularly the moth '' Cactoblastis cactorum''. 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 in April 2012. The

Arabian Peninsula The Arabian Peninsula (, , or , , ) or Arabia, is a peninsula in West Asia, situated north-east of Africa on the Arabian plate. At , comparable in size to India, the Arabian Peninsula is the largest peninsula in the world. Geographically, the ...

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. Pollinating agents can be animals such as insects, for example bees, beetles or butterflies; bird ...

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'' do not open ( cleistogamy). The need to attract

pollinator A pollinator is an animal that moves pollen from the male anther of a flower to the female carpel, stigma of a flower. This helps to bring about fertilization of the ovules in the flower by the male gametes from the pollen grains. Insects are ...

s 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 Pollination, pollen vectors, which can be abiotic (wind and water) or biotic, such as birds, bees, flies, and so forth thro ...

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." Bees 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'' 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.

Hummingbird Hummingbirds are birds native to the Americas and comprise the Family (biology), biological family Trochilidae. With approximately 366 species and 113 genus, genera, they occur from Alaska to Tierra del Fuego, but most species are found in Cen ...

s 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, the face of a human being has a plane of symme ...

, with a lower lip that bends downwards; they produce large amounts of

nectar Nectar is a viscous, sugar-rich liquid produced by Plant, plants in glands called nectaries, either within the flowers with which it attracts pollination, pollinating animals, or by extrafloral nectaries, which provide a nutrient source to an ...

with a relatively low sugar content. ''

'' species, such as '' S. truncata'', have flowers that correspond closely to this syndrome. Other hummingbird-pollinated genera include '' Cleistocactus'' and '' Disocactus''. 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 flying mammals of the order Chiroptera (). 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 birds, flying with their very long spread-out ...

s—an unusually high proportion, exceeded among

eudicots The eudicots or eudicotyledons are flowering plants that have two seed leaves (cotyledons) upon germination. The term derives from ''dicotyledon'' (etymologically, ''eu'' = true; ''di'' = two; ''cotyledon'' = seed leaf). Historically, authors h ...

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'' is an example of a bat-pollinated cactus, as are many species of '' Pachycereus'' and '' Pilosocereus''. Schlumbergera fruit

The

fruit In botany, a fruit is the seed-bearing structure in flowering plants (angiosperms) that is formed from the ovary after flowering. Fruits are the means by which angiosperms disseminate their seeds. Edible fruits in particular have long propaga ...

s 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 are reported to distribute ''Opuntia'' seeds in the Galápagos Islands.

Ant Ants are Eusociality, eusocial insects of the Family (biology), family Formicidae and, along with the related wasps and bees, belong to the Taxonomy (biology), order Hymenoptera. Ants evolved from Vespoidea, vespoid wasp ancestors in the Cre ...

s appear to disperse the seeds of a few genera, such as '' Blossfeldia''. 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

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

, and seeds found in ancient

midden A midden is an old dump for domestic waste. It may consist of animal bones, human excrement, botanical material, mollusc shells, potsherds, lithics (especially debitage), and other artifacts and ecofacts associated with past human oc ...

s (waste dumps) in

Mexico Mexico, officially the United Mexican States, is a country in North America. It is the northernmost country in Latin America, and borders the United States to the north, and Guatemala and Belize to the southeast; while having maritime boundar ...

and

, 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 civilization 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 ...

, whose empire, lasting from the 14th to the 16th century, had a complex system of horticulture. Their capital from the 15th century was

Tenochtitlan , also known as Mexico-Tenochtitlan, was a large Mexican in what is now the historic center of Mexico City. The exact date of the founding of the city is unclear, but the date 13 March 1325 was chosen in 1925 to celebrate the 600th annivers ...

(now

Mexico City Mexico City is the capital city, capital and List of cities in Mexico, largest city of Mexico, as well as the List of North American cities by population, most populous city in North America. It is one of the most important cultural and finan ...

); one explanation for the origin of the name is that it includes the

Nahuatl Nahuatl ( ; ), Aztec, or Mexicano is a language or, by some definitions, a group of languages of the Uto-Aztecan language family. Varieties of Nahuatl are spoken by about Nahuas, most of whom live mainly in Central Mexico and have smaller popul ...

word ''nōchtli'', referring to the fruit of an opuntia. The

coat of arms of Mexico The coat of arms of Mexico (, lit. "national shield of Mexico") is a national symbol of Mexico and depicts a Mexican golden eagle, Mexican (golden) eagle perched on a Opuntia, prickly pear cactus devouring a rattlesnake. The design is rooted in ...

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 The West Indies is an island subregion of the Americas, surrounded by the Atlantic Ocean, North Atlantic Ocean and the Caribbean Sea, which comprises 13 independent island country, island countries and 19 dependent territory, dependencies in thr ...

, 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 head cactus, Turk's cap cactus, or Pope's head cactus, is a genus of cactus with about 30–40 species. They are native to the Caribbean, western Mexico through Central America to northern S ...

''. 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

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'', 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 (

cultivar A cultivar is a kind of Horticulture, cultivated plant that people have selected for desired phenotypic trait, traits and which retains those traits when Plant propagation, propagated. Methods used to propagate cultivars include division, root a ...

s), 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''. 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 Sicily (Italian language, Italian and ), officially the Sicilian Region (), is an island in the central Mediterranean Sea, south of the Italian Peninsula in continental Europe and is one of the 20 regions of Italy, regions of Italy. With 4. ...

Algeria Algeria, officially the People's Democratic Republic of Algeria, is a country in the Maghreb region of North Africa. It is bordered to Algeria–Tunisia border, the northeast by Tunisia; to Algeria–Libya border, the east by Libya; to Alger ...

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 (biology), family Cactaceae), containing species commonly known as chollas ( ), native to northern Mexico and the Southwestern United States. They are known for their barbed thorns, spines, and prick ...

'' species, are also consumed. Almost any fleshy cactus fruit is edible. The word '' pitaya'' 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 () is a hot desert and ecoregion in North America 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 and California). It ...

. 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 ''Stenocereus queretaroensis'' is a species of cactus from Mexico, including the state of Querétaro. It is cultivated for its fruit., pp. 647 Description Plants are tree-like growing with multiple candelabra-shaped branches, up to , with a centr ...

'' is cultivated for its fruit. In more tropical southern areas, the climber '' Selenicereus undatus'' provides ''pitahaya orejona'', now widely grown in Asia under the name dragon fruit. Other cacti providing edible fruit include species of '' Echinocereus'', '' Ferocactus'', ''

'', '' Myrtillocactus'', '' Pachycereus'', '' Peniocereus'' and '' Selenicereus''. The bodies of cacti other than opuntias are less often eaten, although Anderson reported that '' Neowerdermannia vorwerkii'' is prepared and eaten like potatoes in upland Bolivia. Saguaro gatherers2.jpg, Gathering

fruit in 1907 Saguaro fruit.jpg, Edible fruit of the saguaro Barrel Cactus Fruit cropped.jpg, Fruits of some '' Ferocactus'' are edible. Dragonfruit Chiayi market.jpg,

Dragon fruit Pitaya () or pitahaya () (common names strawberry pear or dragon fruit) is the fruit of several cactus species indigenous to the region of southern Mexico and along the Pacific coasts of Guatemala, Costa Rica, and El Salvador. Pitaya is cult ...

for sale in Taiwan Fruto de Stenocereus queretaroensis.jpg, Fruit prepared from ''

'' Nopal11.jpg, Salad including sliced ''nopales'' (

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, ''Trichocereus macrogonus'' var. ''pachanoi'', in South America. Both contain

mescaline Mescaline, also known as mescalin or mezcalin, and in chemical terms 3,4,5-trimethoxyphenethylamine, is a natural product, naturally occurring psychedelic drug, psychedelic alkaloid, protoalkaloid of the substituted phenethylamine class, found ...

. ''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 In cell biology, the meristem is a structure composed of specialized tissue found in plants, consisting of stem cells, known as meristematic cells, which are undifferentiated cells capable of continuous cellular division. These meristematic c ...

), 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 The Catholic Church (), also known as the Roman Catholic Church, is the List of Christian denominations by number of members, largest Christian church, with 1.27 to 1.41 billion baptized Catholics Catholic Church by country, worldwid ...

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 Syncretism, syncretic Native American religion that teaches a combination of traditional Native Americans in the United States, Native American beliefs and eleme ...

. ''Trichocereus macrogonus'' var. ''pachanoi'' (syn. ''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 Saint Peter (born Shimon Bar Yonah; 1 BC – AD 64/68), also known as Peter the Apostle, Simon Peter, Simeon, Simon, or Cephas, was one of the Twelve Apostles of Jesus and one of the first leaders of the Jewish Christian#Jerusalem ekklēsia, e ...

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'' and '' E. lageniformis'', 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

houseplant A houseplant, also known as a pot plant, potted plant, or indoor plant, is an ornamental plant cultivated indoors. for aesthetic or practical purposes. These plants are commonly found in House, homes, Office, offices, and various indoor spaces, w ...

s, 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

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 derived primarily from species of the genus ''Disocactus''. These ''Disocactus'' species are not ...

s, ''

'' (the Thanksgiving or Christmas cactus) and '' Hatiora'' (the Easter cactus), are widely cultivated as houseplants. Gibraltar cactus

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 Xeriscaping is the process of Garden design, landscaping, or gardening, that reduces or eliminates the need for irrigation. It is promoted in regions that do not have accessible, plentiful, or reliable supplies of fresh water and has gained acce ...

). For example, in

California California () is a U.S. state, state in the Western United States that lies on the West Coast of the United States, Pacific Coast. It borders Oregon to the north, Nevada and Arizona to the east, and shares Mexico–United States border, an ...

, 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 Herbal medicine (also called herbalism, phytomedicine or phytotherapy) is the study of pharmacognosy and the use of medicinal plants, which are a basis of traditional medicine. Scientific evidence for the effectiveness of many herbal treatments ...

. 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 India, officially the Republic of India, is a country in South Asia. It is the List of countries and dependencies by area, seventh-largest country by area; the List of countries by population (United Nations), most populous country since ...

is a red dye produced by a

scale insect Scale insects are small insects of the Order (biology), order Hemiptera, suborder Sternorrhyncha. Of dramatically variable appearance and extreme sexual dimorphism, they comprise the infraorder Coccomorpha which is considered a more convenient g ...

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 animals. The woody parts of cacti, such as '' Cereus repandus'' and '' Echinopsis atacamensis'', are used in buildings and in furniture. The frames of

wattle and daub Wattle and daub is a composite material, composite building method in which a woven lattice of wooden strips called "wattle (construction), wattle" is "daubed" with a sticky material usually made of some combination of wet soil, clay, sand, and ...

houses built by the

Seri people The Seri or ''Comcaac'' people are an Indigenous group of the Mexican state of Sonora. The majority reside on the Seri communal property (), in the towns of Punta Chueca () and El Desemboque () on the mainland coast of the Gulf of California ...

of Mexico may use parts of the

(''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), 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'' and '' Discocactus'' 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,

, caused the destruction of a large part of the natural habitat of ''

Echinocactus grusonii ''Kroenleinia grusonii'', popularly known as the golden barrel cactus, golden ball, "mother-in-law's cushion" or "mother-in-law’s chair", is a species of barrel cactus which is endemism, endemic to east-central Mexico. The golden barrel cactus ...

''. Urban development and highways have destroyed cactus habitats in parts of Mexico,

New Mexico New Mexico is a state in the Southwestern United States, Southwestern region of the United States. It is one of the Mountain States of the southern Rocky Mountains, sharing the Four Corners region with Utah, Colorado, and Arizona. It also ...

and

Arizona Arizona is a U.S. state, state in the Southwestern United States, Southwestern region of the United States, sharing the Four Corners region of the western United States with Colorado, New Mexico, and Utah. It also borders Nevada to the nort ...

, including the

. The conversion of land to agriculture has affected populations of '' Ariocarpus kotschoubeyanus'' in Mexico, where dry plains were plowed for maize cultivation, and of '' Copiapoa'' and '' Eulychnia'' in

, 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 () are an archipelago of volcanic islands in the Eastern Pacific, located around the equator, west of the mainland of South America. They form the Galápagos Province of the Republic of Ecuador, with a population of sli ...

generally and the effect on '' Browningia candelaris'' in

. Over-collection of cacti for sale has greatly affected some species. For example, the type locality of '' Pelecyphora strobiliformis'' near Miquihuana, 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 a List of national parks of the United States, national park of the United States located in West Texas, bordering Mexico. The park has national significance as the largest protected area of Chihuahuan Desert topograph ...

, Texas;

Joshua Tree National Park Joshua Tree National Park is a List of national parks of the United States, US National Park located in southeastern California, straddling north-central Riverside County, California, Riverside County and part of southern San Bernardino County, ...

, California; and

Saguaro National Park Saguaro National Park is a List of national parks of the United States, national park of the United States in southeastern Arizona. The park consists of two separate areas—the Tucson Mountain District (TMD), about west of Tucson, Arizona, T ...

, Arizona. Latin American examples include El Pinacate y Gran Desierto de Altar Biosphere Reserve, 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, 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 Schlumbergera#Cultivation, Cultivation of ''Schlumbergera'' (Christmas or Thanksgiving cacti), and Epiphyllum hybrid#Cultivation, 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", 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 ''

'' and '' Discocactus''. Some cacti, particularly those from the high

, are fully frost-hardy when kept dry (e.g. ''Rebutia minuscula'' survives temperatures down to in cultivation) and may flower better when exposed to a period of cold.

Propagation

Cacti can be propagated by seed, Cutting (plant), 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 is needed to conditions in a greenhouse, such as higher temperatures and strong sunlight. PikiWiki Israel 14907 The Cactus Avenue

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 (cell biology), callus forms over the cut surface. Rooting can then take place in an appropriate growing medium at a temperature of around . Trichocereus bridgesii

Grafting is used for species difficult to grow well in cultivation or that cannot grow independently, such as some

-free forms with white, yellow or red bodies, or some forms that show abnormal growth (e.g., Fasciation, cristate or forms). For the host plant (the stock (grafting), stock), growers choose one that grows strongly in cultivation and is compatible with the plant to be propagated: the scion (grafting), scion. 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 mealybugs, living on both stems and roots;

s, generally only found on stems; whitefly, whiteflies, which are said to be an "infrequent" pest of cacti; Tetranychus urticae, 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 Insecticide resistance, resistant to many insecticides, although there are biological controls available. Roots of cacti can be eaten by the larvae of Sciaridae, sciarid flies and fungus gnats. Slugs and snails also eat cacti. Fungi, bacteria and viruses attack cacti, the first two particularly when plants are over-watered. Fusarium oxysporum, 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 (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 viral diseases.

Notes

References

Bibliography

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External links

* * {{Authority control Cacti, Drought-tolerant plants Eocene plants Priabonian first appearances Extant Eocene first appearances Taxa named by Carl Linnaeus