Aloeae

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Aloeae
Aloe speciosa - tilt head aloe.jpg
Aloe speciosa
Scientific classification Red Pencil Icon.png
Kingdom: Plantae
Clade: Tracheophytes
Clade: Angiosperms
Clade: Monocots
Order: Asparagales
Family: Asphodelaceae
Subfamily: Asphodeloideae
Tribe: Aloeae
A.Rich. [1]
Genera

See text.

Aloeae is a tribe of succulent plants in the subfamily Asphodeloideae of the family Asphodelaceae, consisting of the aloes and their close relatives. The taxon may also be treated as the subfamily Alooideae by those botanists who retain the narrower circumscription of Asphodelaceae adopted prior to the APG III system. Typically, plants have rosettes of more or less succulent leaves, with or without a distinct stem. Their flowers are arranged in racemes and tend to be either small and pale, pollinated by insects, or larger and more brightly coloured, pollinated by birds. As of 2017, 11 genera are recognized, most created since 2010 by splitting off another five genera from Aloe and another two from Haworthia . Only two genera, Aloe and Aloidendron , are native outside southern Africa, extending northwards to the Arabian Peninsula. Seven genera are restricted to South Africa, 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 and Aloe ferox are cultivated for their extracts, whose uses include moisturizers and emollients in cosmetics.

Contents

Description

Aloeae leaves are more or less succulent 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 tubercules. 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 for all Aloeae taxa. [2]

The inflorescence is compacted into a many-flowered spike, or a simple or branched raceme, and is apical, although it can seem axillary. Stems are monopodial (unbranched) until an inflorescence is formed, and then sympodial (potentially branched); this prevents the rosette from dying as in Agave . Flowers of all taxa within Aloeae are tubular and have some fusion of petal-like tepals, although the amount of fusion varies among genera. [2] Differences in flower structure and colour among genera are considered to represent pollination syndromes, 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. [3]

Variation in Astroloba flowers associated with different pollinators

Within the subfamily Asphodeloideae, Aloeae can be diagnosed by their succulent foliage, a basic chromosome number of x = 7, and the presence of specific glycosides in the leaves and anthraquinones in the roots. [3]

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 followed authors before him in using a single genus, Aloe, for all the "aloes" known to him. [4] The genus was subsequently split several times; for example, Kumara was separated out in 1786, Haworthia and Gasteria in 1809. [3] Regardless of the number of genera, the "aloes" were placed in the family Liliaceae, formally described by Antoine Laurent de Jussieu in 1789. The Liliaceae sensu lato grew in scope until it included most of the lilioid monocots. [5] Attempts were made to carve out separate families. In 1802, August Batsch placed the "aloes" in the family Aloaceae rather than the Liliaceae. However, his family was rarely adopted by other botanists. [6] [7]

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. [6] [5] This sense of the Asphodelaceae was supported by the first APG system of 1998. However, the Angiosperm Phylogeny Group later adopted a broader circumscription, so that in the APG IV system of 2016, the Asphodelaceae sensu stricto becomes the subfamily Asphodeloideae of the Asphodelaceae sensu lato. [8] 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. [3]

Alternative classifications of the "aloes"
Family: Asphodelaceae sensu APG IV
Subfamily: AsphodeloideaeFamily: Asphodelaceae sensu stricto
Tribe: AloeaeA.Rich.Subfamily: Alooideae Link [6]
informally "alooids"

Phylogeny

Four genera, Aloe , Haworthia , Gasteria 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 and coworkers produced a phylogeny based on 11 genera. Aloe was divided into six genera, and Haworthia into three: [3]

Aloeae

Aloidendron = Aloe sect. Aloidendron + sect. Dracoaloe

Kumara = Aloe sect. Kumara + sect. Haemanthifoliae

Haworthia = Haworthia subg. Haworthia

Aloiampelos = Aloe sect. Macrifoliae

Aloe

TR

Astroloba

Aristaloe = Aloe sect. Aristatae

Gonialoe = Aloe sect. Serrulatae

Tulista = Haworthia subg. Robustipedunculatae

Haworthiopsis = Haworthia subg. Hexangulares

Gasteria

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. [3]

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. [9] This was rejected by Manning et al., but has since been defended by Rowley. [10]

Genera

As of October 2017, the tribe consisted of the following genera. [3] Native distributions are based on the World Checklist of Selected Plant Families; many genera are widely cultivated and introduced elsewhere. [11]

Diversity of Aloeae genera

Distribution and habitat

The largest genus, Aloe, with about 400 species, is natively distributed in Africa (including Madagascar), and in the Arabian Peninsula. 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, 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. [12] Many species are cultivated as ornamental plants, and Aloe species in particular have become widely naturalized. [13]

Uses

Many species are cultivated by succulent plant enthusiasts; Aloe species in particular are used in temperate climates as ornamental garden plants. [14] Aloe vera and Aloe ferox are used in traditional medicine and cosmetics for their moisturizing and emollient effects. [15] [14] Industries based on these two species were reported to be worth "millions of dollars per year" in South Africa alone. [14] Injured leaves of many species of Aloe exude a gel that contains aloin (also known as barbaloin). Aloin has been used as a laxative, [16] [17] and also to add a bitter taste to foods. [18] Some species of Haworthia and Gasteria are also used in traditional medicine. [14]

Related Research Articles

<i>Aloe</i> Genus of succulent flowering plants

Aloe is a genus containing over 650 species of flowering succulent plants. The most widely known species is Aloe vera, or "true aloe". It is called this because it is cultivated as the standard source for assorted pharmaceutical purposes. Other species, such as Aloe ferox, are also cultivated or harvested from the wild for similar applications.

<span class="mw-page-title-main">Asphodeloideae</span> Subfamily of flowering plants, in monocot family Asphodelaceae

Asphodeloideae is a subfamily of the monocot family Asphodelaceae in the order Asparagales. It has previously been treated as a separate family, Asphodelaceae sensu stricto. The family Asphodelaceae has now been proposed to be a nomen conservandum, and the proposal has been recommended for ratification in 2017. In that case, Asphodelaceae will have priority over Xanthorrhoeaceae. This is reflected in the APG IV family lists.

<span class="mw-page-title-main">Asphodelaceae</span> Family of flowering plants in the order Asparagales

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 40 genera and 900 known species. The type genus is Asphodelus.

<i>Aristaloe</i> Monotypic genus of flowering perennial plant from southern Africa

Aristaloe is a genus of evergreen flowering perennial plants in the family Asphodelaceae from Southern Africa. Its sole species is Aristaloe aristata, known as guinea-fowl aloe or lace aloe.

<i>Haworthia</i> Genus of flowering plants

Haworthia is a large genus of small succulent plants endemic to Southern Africa (Mozambique, Namibia, Lesotho, Eswatini and South Africa).

<i>Gasteria</i> Genus of succulent flowering plants from South Africa

Gasteria is a genus of succulent plants, native to South Africa.

<i>Aloidendron barberae</i> Species of tree

Aloidendron barberae, formerly Aloe bainesii and Aloe barberae, also known as the tree aloe, is a species of succulent plant in the genus Aloidendron. It is native to South Africa northwards to Mozambique. In its native climes this slow-growing tree can reach up to 60 feet (18 m) high and 36 inches (0.91 m) in stem diameter. Aloidendron barberae is Africa's largest aloe-like plant. The tree aloe is often used as an ornamental plant. Its tubular flowers are rose pink (green-tipped); it flowers in winter and in its natural environment is pollinated by sunbirds.

<i>Astroloba rubriflora</i> Species of flowering plant

Astroloba rubriflora is a succulent plant found in the mountainous Karoo area around Robertson, South Africa. It is listed as a Vulnerable species on the IUCN global Red List.

<i>Haworthiopsis venosa</i> Species of succulent

Haworthiopsis venosa, formerly Haworthia venosa, known in Afrikaans as venstertjie, is a species of flowering plant in the genus Haworthiopsis belonging to the family Asphodelaceae, native to Namibia and South Africa.

<i>Astroloba</i> Genus of flowering plants native to South Africa

Astroloba is a genus of flowering plants in the family Asphodelaceae, subfamily Asphodeloideae, native to the Cape Province of South Africa.

<i>Tulista</i> Genus of flowering plants

Tulista is a small genus of succulent plants endemic to South Africa. They were formerly included within the genus Haworthia.

<i>Kumara</i> (plant) Genus of flowering plants

Kumara is a genus of two species of flowering plants in the subfamily Asphodeloideae, native to the Western Cape Province of South Africa.

<i>Haworthiopsis pungens</i> Species of succulent

Haworthiopsis pungens, formerly Haworthia pungens, is a species of flowering succulent plant from the Eastern Cape Province, South Africa.

<i>Haworthiopsis viscosa</i> Species of succulent

Haworthiopsis viscosa, formerly Haworthia viscosa, is a species of flowering succulent plant from the Western and Eastern Cape Provinces, South Africa.

<i>Tulista pumila</i> Species of flowering plant

Tulista pumila ("Vratjiesaalwee") is a species of Tulista succulent plant, from the Western Cape, South Africa.

<i>Tulista kingiana</i> Species of succulent plant from the Western Cape, South Africa

Tulista kingiana is a species of succulent plant, from the Western Cape, South Africa. It is listed as Endangered on the IUCN global Red List

<i>Gonialoe</i> Genus of succulent flowering plants from southern Africa

Gonialoe is a small genus of three succulent plant species, indigenous to South Africa, Namibia and Angola. They were formerly included within the related genus Aloe. The three species are Gonialoe variegata, Gonialoe sladeniana, Gonialoe dinteri.

<i>Aloidendron</i> Species of plant in the family Asphodelaceae

Aloidendron is a genus of succulent plants in the subfamily Asphodeloideae. It was split off from the much larger genus Aloe in 2013.

<i>Haworthiopsis</i> Genus of succulent plants

Haworthiopsis is a genus of succulent plants in the subfamily Asphodeloideae. The genus was previously included in Haworthia. Species in the genus are typically short perennial plants, with leaves often arranged in a rosette and frequently having raised white markings. The two-lipped flowers are borne on a tall stalk and are small – less than 17 mm (0.7 in) long – and pale in colour. Many species are cultivated as house plants or by succulent enthusiasts.

References

  1. ↑ Reveal, James L. (2011), Indices Nominum Supragenericorum Plantarum Vascularium – A , retrieved 2017-10-19
  2. 1 2 Smith, G.F.; Van Wyk, B.E. (1991), "Generic Relationships in the Alooideae (Asphodelaceae)", Taxon, 40 (4): 557–581, doi:10.2307/1222765, JSTOR   1222765
  3. 1 2 3 4 5 6 7 Manning, John; Boatwright, James S.; Daru, Barnabas H.; Maurin, Olivier & Bank, Michelle van der (2014), "A Molecular Phylogeny and Generic Classification of Asphodelaceae Subfamily Alooideae: A Final Resolution of the Prickly Issue of Polyphyly in the Alooids?", Systematic Botany, 39 (1): 55–74, doi:10.1600/036364414X678044, S2CID   86714657 , retrieved 2017-10-22
  4. ↑ Gildenhuys, Sean D. & Klopper, Ronell R. (2016), "A synoptic review and new infrageneric classification for the genus Haworthiopsis (Xanthorrhoeaceae: Asphodeloideae)" (PDF), Phytotaxa, 265 (1): 1–26, doi:10.11646/phytotaxa.265.1.1, hdl: 2263/57046 , retrieved 2017-10-18
  5. 1 2 Kelch, D.G. (2002), "Consider the Lilies" (PDF), Fremontia, 30 (2): 23–29
  6. 1 2 3 Smith, Gideon F. (1993), "Familial Orthography: Aloeaceae vs. Aloaceae", Taxon, 42 (1): 87–90, doi:10.2307/1223308, JSTOR   1223308
  7. ↑ Holmes, Walter C. & White, Heather L., "Aloaceae", in Flora of North America Editorial Committee (ed.), Flora of North America (online), eFloras.org, retrieved 2017-10-19
  8. ↑ Angiosperm Phylogeny Group (2009), "An update of the Angiosperm Phylogeny Group classification for the orders and families of flowering plants: APG III", Botanical Journal of the Linnean Society, 161 (2): 105–121, doi: 10.1111/j.1095-8339.2009.00996.x
  9. ↑ Rowley, G.D. (2013), "Generic concepts in the Alooideae 3: The phylogenetic story", Alsterworthia International Special Issue, 10: 1–7; cited in Gildenhuys & Klopper (2016) {{citation}}: CS1 maint: postscript (link)
  10. ↑ Rowley, Gordon (2015), "Tulista Raf. - Counsel for the Defence" (PDF), Alsterworthia, 15 (1): 2–3, retrieved 2017-10-20
  11. ↑ "Taxon search", World Checklist of Selected Plant Families , Royal Botanic Gardens, Kew , retrieved 2017-10-19
  12. ↑ Manning, John C.; Boatwright, James S. & Daru, Barnabas H. (2014), "Aloe and goodbye: a new evolutionary classification of the Alooids", Alsterworthia International, 14 (2): 7–15, retrieved 2017-10-19
  13. ↑ "Aloe", World Checklist of Selected Plant Families, Royal Botanic Gardens, Kew , retrieved 2017-10-19
  14. 1 2 3 4 Smith, G.F. & Newton, L.E. (2002) [copyright 2001], "Aloaceae", in Eggli, Urs (ed.), Illustrated Handbook of Succulent Plants: Monocotyledons, Berlin: Springer-Verlag, p. 102ff, ISBN   978-3-540-41692-0 , retrieved 2017-10-19
  15. ↑ Eshun, K. & He, Q. (2004), "Aloe vera: a valuable ingredient for the food, pharmaceutical and cosmetic industries—a review", Crit Rev Food Sci Nutr, 44 (2): 91–6, doi:10.1080/10408690490424694, PMID   15116756, S2CID   21241302
  16. ↑ Ishii, Y.; Tanizawa, H. & Takino, Y. (1994), "Studies of aloe. V. Mechanism of cathartic effect (4)", Biological and Pharmaceutical Bulletin, 17 (5): 651–653, doi: 10.1248/bpb.17.651 , PMID   7920425
  17. ↑ Lulinski, Beth & Kapica, Cathy (1998), "Some notes on Aloe Vera", Quackwatch, retrieved 2017-10-19
  18. ↑ IARC Working Group on the Evaluation of Carcinogenic Risk to Humans (2016), "1 Exposure Data", Some Drugs and Herbal Products, IARC Monographs on the Evaluation of Carcinogenic Risks to Humans, No. 108, Lyon: International Agency for Research on Cancer, retrieved 2017-10-19
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