Aloeae
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Aloeae is a
tribe The term tribe is used in many different contexts to refer to a category of human social group. The predominant worldwide use of the term in English is in the discipline of anthropology. The definition is contested, in part due to conflict ...
of
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 the subfamily Asphodeloideae of the family
Asphodelaceae Asphodelaceae is a family of flowering plants in the order Asparagales. Such a family has been recognized by most taxonomists, but the circumscription has varied widely. In its current circumscription in the APG IV system, it includes about 4 ...
, consisting of the aloes and their close relatives. The
taxon In biology, a taxon (back-formation from ''taxonomy''; : taxa) is a group of one or more populations of an organism or organisms seen by taxonomists to form a unit. Although neither is required, a taxon is usually known by a particular name and ...
may also be treated as the subfamily Alooideae by those botanists who retain the narrower
circumscription Circumscription may refer to: * Circumscribed circle * Circumscription (logic) *Circumscription (taxonomy) * Circumscription theory, a theory about the origins of the political state in the history of human evolution proposed by the American anthr ...
of Asphodelaceae adopted prior to the
APG III system The APG III system of flowering plant classification is the third version of a modern, mostly molecular-based, system of plant taxonomy being developed by the Angiosperm Phylogeny Group (APG). Published in 2009, it was superseded in 2016 by a f ...
. Typically, plants have rosettes of more or less succulent leaves, with or without a distinct stem. Their flowers are arranged in
raceme A raceme () or racemoid is an unbranched, indeterminate growth, indeterminate type of inflorescence bearing flowers having short floral stalks along the shoots that bear the flowers. The oldest flowers grow close to the base and new flowers are ...
s and tend to be either small and pale, pollinated by insects, or larger and more brightly coloured, pollinated by birds. , 11
genera Genus (; : genera ) is a taxonomic rank above species and below family as used in the biological classification of living and fossil organisms as well as viruses. In binomial nomenclature, the genus name forms the first part of the binomial s ...
are recognized, most created since 2010 by splitting off another five genera from ''
Aloe ''Aloe'' (; also written ''Aloë'') is a genus containing over 650 species of flowering plant, flowering succulent plant, succulent plants.WFO (2022): Aloe L. Published on the Internet;http://www.worldfloraonline.org/taxon/wfo-4000001341. Acc ...
'' and another two from ''
Haworthia ''Haworthia'' is a large genus of small succulent plants endemic to Southern Africa (Mozambique, Namibia, Lesotho, Eswatini and South Africa). Like aloes and gasteria they are members of the Family (biology), subfamily Asphodeloideae and they ...
''. Only two genera, ''Aloe'' and '' Aloidendron'', are native outside southern Africa, extending northwards to 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 ...
. Seven genera are restricted to
South Africa South Africa, officially the Republic of South Africa (RSA), is the Southern Africa, southernmost country in Africa. Its Provinces of South Africa, nine provinces are bounded to the south by of coastline that stretches along the Atlantic O ...
, some with small ranges. Members of the Aloeae are cultivated by succulent plant enthusiasts; ''Aloe'' species especially are used in temperate climates as ornamental garden plants. Some species are used in traditional medicine. ''
Aloe vera ''Aloe vera'' () is a succulent plant species of the genus ''Aloe''. It is widely distributed, and is considered an invasive species in many world regions. An evergreen perennial plant, perennial, it originates from the Arabian Peninsula, but ...
'' and '' Aloe ferox'' are cultivated for their extracts, whose uses include moisturizers and emollients in cosmetics.


Description

Aloeae leaves are more or less
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 ...
and arranged in strongly tufted terminal rosettes (in arborescent species, as in '' Aloidendron barberae'') or in basal rosettes, and are organized in distinct ranks. Leaves are succulent and have distinctive white or other uniformly coloured
tubercule In anatomy, a tubercle (literally 'small tuber', Latin for 'lump') is any round nodule, small eminence, or warty outgrowth found on external or internal organs of a plant or an animal. In plants A tubercle is generally a wart-like projection, ...
s. This is hypothesized to be a derived condition, possibly as a mechanical defensive mechanism to make the leaf less palatable, or to prevent heat damage in arid conditions. The cross-section of the leaves is distinctly boat or crescent shaped, which represents a
synapomorphy In phylogenetics, an apomorphy (or derived trait) is a novel Phenotypic trait, character or character state that has evolution, evolved from its ancestral form (or Plesiomorphy and symplesiomorphy, plesiomorphy). A synapomorphy is an apomorphy sh ...
for all Aloeae
taxa In biology, a taxon (back-formation from ''taxonomy''; : taxa) is a group of one or more populations of an organism or organisms seen by taxonomists to form a unit. Although neither is required, a taxon is usually known by a particular name and ...
. The
inflorescence In botany, an inflorescence is a group or cluster of flowers arranged on a plant's Plant stem, stem that is composed of a main branch or a system of branches. An inflorescence is categorized on the basis of the arrangement of flowers on a mai ...
is compacted into a many-flowered spike, or a simple or branched
raceme A raceme () or racemoid is an unbranched, indeterminate growth, indeterminate type of inflorescence bearing flowers having short floral stalks along the shoots that bear the flowers. The oldest flowers grow close to the base and new flowers are ...
, and is apical, although it can seem axillary. Stems are
monopodial Vascular plants with monopodial growth habits grow upward from a single point. They add leaves to the apex each year and the stem grows longer accordingly. The word ''Monopodial'' is derived from Greek language, Greek '', ''one'' and '', "foot", in ...
(unbranched) until an inflorescence is formed, and then
sympodial In botany, sympodial growth is a bifurcating branching pattern where one branch develops more strongly than the other, resulting in the stronger branches forming the primary shoot and the weaker branches appearing laterally. A sympodium, als ...
(potentially branched); this prevents the rosette from dying as in ''
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 ...
''. Flowers of all taxa within Aloeae are tubular and have some fusion of petal-like
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, although the amount of fusion varies among genera. Differences in flower structure and colour among genera are considered to represent
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, particularly shifts between insect and bird pollination, and so are less reliable indicators of relationships among species than was once thought. Thus '' Astroloba corrugata'', like most species of '' Astroloba'', has small, pale, horizontally held flowers that are insect-pollinated, whereas '' A. rubriflora'' has larger, red, vertically held flowers that are bird-pollinated. File:Astroloba corrugata - detail of inflorescence 4.jpg, '' Astroloba corrugata'' – insect-pollinated flowers File:Astroloba rubriflora - poellnitzia flowers McGregor South Africa.jpg, '' Astroloba rubriflora'' – bird-pollinated flowers Within the subfamily Asphodeloideae, Aloeae can be diagnosed by their succulent foliage, a basic
chromosome number Ploidy () is the number of complete sets of chromosomes in a cell, and hence the number of possible alleles for autosomal and pseudoautosomal genes. Here ''sets of chromosomes'' refers to the number of maternal and paternal chromosome copies, ...
of x = 7, and the presence of specific
glycoside In chemistry, a glycoside is a molecule in which a sugar is bound to another functional group via a glycosidic bond. Glycosides play numerous important roles in living organisms. Many plants store chemicals in the form of inactive glycosides. ...
s in the leaves and anthraquinones in the roots.


Taxonomy

The unity of this group of plants, the "aloes", has long been recognized, although its classification and nomenclature have varied considerably. In 1753,
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 ...
followed authors before him in using a single genus, ''Aloe'', for all the "aloes" known to him. The genus was subsequently split several times; for example, ''Kumara'' was separated out in 1786, ''Haworthia'' and ''Gasteria'' in 1809. Regardless of the number of genera, the "aloes" were placed in the family Liliaceae, formally described by
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 ...
in 1789. The Liliaceae ''
sensu lato ''Sensu'' is a Latin word meaning "in the sense of". It is used in a number of fields including biology, geology, linguistics, semiotics, and law. Commonly it refers to how strictly or loosely an expression is used in describing any particular co ...
'' grew in scope until it included most of the
lilioid monocots Lilioid monocots (lilioids, liliid monocots, petaloid monocots, petaloid lilioid monocots) is an informal name used for a grade (biology), grade (grouping of taxa with common characteristics) of five monocot order (biology), orders (Petrosavial ...
. Attempts were made to carve out separate families. In 1802,
August Batsch August Johann Georg Karl Batsch (28 October 1761 – 29 September 1802) was a German naturalist. He was a recognised authority on mushrooms, and also described new species of ferns, bryophytes, and seed plants. Life and career Batsch was born ...
placed the "aloes" in the family Aloaceae rather than the Liliaceae. However, his family was rarely adopted by other botanists. The Dahlgren system of 1975 onwards was one of the first to produce a classification more in line with current understanding; it placed the "aloes" in the family Asphodelaceae, with the subfamily Alooideae more-or-less corresponding to Batsch's Aloaceae. This sense of the Asphodelaceae was supported by the first
APG system The APG system (Angiosperm Phylogeny Group system) of plant classification is the first version of a modern, mostly molecular-based, system of plant taxonomy. Published in 1998 by the Angiosperm Phylogeny Group, it was replaced by the improved ...
of 1998. However, the
Angiosperm Phylogeny Group The Angiosperm Phylogeny Group (APG) is an informal international group of systematic botanists who collaborate to establish a consensus on the taxonomy of flowering plants (angiosperms) that reflects new knowledge about plant relationships disc ...
later adopted a broader
circumscription Circumscription may refer to: * Circumscribed circle * Circumscription (logic) *Circumscription (taxonomy) * Circumscription theory, a theory about the origins of the political state in the history of human evolution proposed by the American anthr ...
, so that in the
APG IV system The APG IV system of flowering plant classification is the fourth version of a modern, mostly molecular-based, system of plant taxonomy for flowering plants (angiosperms) being developed by the Angiosperm Phylogeny Group (APG). It was publish ...
of 2016, the Asphodelaceae ''sensu stricto'' becomes the subfamily Asphodeloideae of the Asphodelaceae ''sensu lato''. In this system, the "aloes" form the tribe Aloeae. However, the APG's approach has not been followed by many botanists, who prefer to maintain the older, narrower circumscription of the Asphodelaceae, with the "aloes" forming the subfamily Alooideae.


Phylogeny

Four genera, ''
Aloe ''Aloe'' (; also written ''Aloë'') is a genus containing over 650 species of flowering plant, flowering succulent plant, succulent plants.WFO (2022): Aloe L. Published on the Internet;http://www.worldfloraonline.org/taxon/wfo-4000001341. Acc ...
'', ''
Haworthia ''Haworthia'' is a large genus of small succulent plants endemic to Southern Africa (Mozambique, Namibia, Lesotho, Eswatini and South Africa). Like aloes and gasteria they are members of the Family (biology), subfamily Asphodeloideae and they ...
'', ''
Gasteria ''Gasteria'' is a genus of succulent plants, native to South Africa and the far south-west corner of Namibia. Naming The genus is named for its stomach-shaped flowers (''"gaster"'' is Greek for "stomach") that result from the swollen base on the ...
'' and '' Astroloba'', were considered "core" members of the tribe, ''Aloe'' being by far the largest genus. The genera were difficult to characterize based purely on morphological characters. ''Aloe'' in particular had few if any obvious distinctive derived characters. Molecular phylogenetic studies, particularly from 2010 onwards, suggested that the tribe should be divided into more tightly defined genera. In 2014,
John Charles Manning John Charles Manning (born 1962) is a South African botanist based in the Compton Herbarium, South African National Biodiversity Institute The South African National Biodiversity Institute (SANBI) is an organisation tasked with research an ...
and coworkers produced a phylogeny based on 11 genera. ''Aloe'' was divided into six genera, and ''Haworthia'' into three: More detailed cladograms show that some species placed in ''Haworthiopsis'' do not fit into the tidy pattern above. ''Haworthia koelmaniorum'' falls outside the main ''Haworthiopsis'' clade in one analysis, but was placed in that genus on the basis of other evidence. ''H. attenuata'' and ''H. venosa'', also placed in ''Haworthiopsis'', form a clade that is weakly placed as sister to the combination of the main ''Haworthiopsis'' clade plus ''Gasteria''. Gordon Rowley, who first separated off ''Haworthiopsis'' from ''Haworthia'' in 2013, suggested a much broader circumscription of ''Tulista'' – essentially as the clade marked "TR" in the above cladogram. This was rejected by Manning et al., but has since been defended by Rowley.


Genera

, the tribe consisted of the following genera. Native distributions are based on the
World Checklist of Selected Plant Families The World Checklist of Selected Plant Families (usually abbreviated to WCSP) was an "international collaborative programme that provides the latest peer reviewed and published opinions on the accepted scientific names and synonyms of selected p ...
; many genera are widely cultivated and introduced elsewhere. *''
Aloe ''Aloe'' (; also written ''Aloë'') is a genus containing over 650 species of flowering plant, flowering succulent plant, succulent plants.WFO (2022): Aloe L. Published on the Internet;http://www.worldfloraonline.org/taxon/wfo-4000001341. Acc ...
'' L. – Tropical Africa, South Africa, Madagascar, Jordan to the Arabian Peninsula *'' Aloiampelos'' Klopper & Gideon F.Sm. – South Africa *'' Aloidendron'' (A. Berger) Klopper & Gideon F.Sm. – south-west Arabian Peninsula, Somalia, Mozambique to South Africa *'' Aristaloe'' Boatwr. & J.C.Manning – South Africa *'' Astroloba'' Uitewaal – South Africa (
Cape Provinces The Cape Provinces of South Africa is a biogeographical area used in the World Geographical Scheme for Recording Plant Distributions (WGSRPD). It is part of the WGSRPD region 27 Southern Africa. The area has the code "CPP". It includes the Sou ...
) *''
Gasteria ''Gasteria'' is a genus of succulent plants, native to South Africa and the far south-west corner of Namibia. Naming The genus is named for its stomach-shaped flowers (''"gaster"'' is Greek for "stomach") that result from the swollen base on the ...
'' Duval – South Africa *'' Gonialoe'' (Baker) Boatwr. & J.C.Manning – Angola, Namibia, South Africa *''
Haworthia ''Haworthia'' is a large genus of small succulent plants endemic to Southern Africa (Mozambique, Namibia, Lesotho, Eswatini and South Africa). Like aloes and gasteria they are members of the Family (biology), subfamily Asphodeloideae and they ...
'' Duval – South Africa *'' Haworthiopsis'' G.D.Rowley – Eswatini, Mozambique, Namibia, South Africa *'' Kumara'' Medik. – South Africa (south-west Cape Provinces) *''
Tulista ''Tulista'' is a small genus of succulent plants endemic to the Cape Provinces of South Africa. They were formerly included within the genus ''Haworthia''. Characteristics The genus is characterised by a large size (relative to other haworthias) ...
'' Raf. – South Africa (Cape Provinces) Aloe cameronii - Vumba 2 (10246529833).jpg, '' Aloe cameronii'' Aloe tenuior var tenuior - South Africa 3.JPG, '' Aloiampelos tenuior'' QuiverTree-Namibia-2015.JPG, '' Aloidendron dichotomum'' AloeAristata.jpg, '' Aristaloe aristata'' Astroloba foliolosa - South African Succulent.jpg, '' Astroloba foliolosa'' Gasteria disticha 001.jpg, '' Gasteria disticha'' Aloe_variegata.jpg, '' Gonialoe variegata'' Haworthia bayeri in habitat South Africa 1.jpg, '' Haworthia bayeri'' Ab plant 846.jpg, '' Haworthiopsis attenuata'' 1 Aloe plicatilis - Fan Aloe of South Africa 1.jpg, ''
Kumara plicatilis ''Kumara plicatilis'', formerly ''Aloe plicatilis'', the fan-aloe, is a succulent plant endemic to a few mountains in the Fynbos ecoregion, of the Western Cape in South Africa. The plant has an unusual and striking fan-like arrangement of its leav ...
'' Haworthia minima MBB 7.jpg, '' Tulista minima''


Distribution and habitat

The largest genus, ''Aloe'', with about 400 species, is natively distributed in Africa (including
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 in 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 ...
. ''Aloidendron'', with six or seven species, also has a quite wide native distribution in southern and east Africa extending northwards to the Arabian Peninsula. The remaining genera are native only to
southern Africa Southern Africa is the southernmost region of Africa. No definition is agreed upon, but some groupings include the United Nations geoscheme for Africa, United Nations geoscheme, the intergovernmental Southern African Development Community, and ...
, some being restricted to a few locations in South Africa. ''Kumara'', ''Haworthia'', ''Astroloba'', ''Tulista'' and ''Haworthiopsis'' are found in winter rainfall areas of southern Africa. ''Gonialoe'' species are found in arid regions of South Africa and Namibia. Many species are cultivated as ornamental plants, and ''Aloe'' species in particular have become widely naturalized.


Uses

Many species are cultivated by succulent plant enthusiasts; ''Aloe'' species in particular are used in temperate climates as ornamental garden plants. ''
Aloe vera ''Aloe vera'' () is a succulent plant species of the genus ''Aloe''. It is widely distributed, and is considered an invasive species in many world regions. An evergreen perennial plant, perennial, it originates from the Arabian Peninsula, but ...
'' and '' Aloe ferox'' are used in traditional medicine and cosmetics for their moisturizing and emollient effects. Industries based on these two species were reported to be worth "millions of dollars per year" in South Africa alone. Injured leaves of many species of ''Aloe'' exude a gel that contains
aloin Aloin, also known as barbaloin, is a bitter, yellow-brown colored compound noted in the exudate of at least 68 ''Aloe'' species at levels from 0.1 to 6.6% of leaf dry weight (making between 3% and 35% of the total exudate), and in another 17 spec ...
(also known as barbaloin). Aloin has been used as a
laxative Laxatives, purgatives, or aperients are substances that loosen stools and increase bowel movements. They are used to treat and prevent constipation. Laxatives vary as to how they work and the side effects they may have. Certain stimulant, lubri ...
, and also to add a bitter taste to foods. Some species of ''Haworthia'' and ''Gasteria'' are also used in traditional medicine.


References

{{taxonbar, from1=Q48790477 Asphodeloideae Asparagales tribes