L., Sp. Pl., 1: 319, 1753 
Aloe pron.: //, also Aloë, is a genus containing about 500 species of flowering succulent plants. The most widely known species is Aloe vera, or "true aloe", so called because, though probably extinct in the wild, it is cultivated as the standard source of so-called "aloe vera" for assorted pharmaceutical purposes. Other species, such as Aloe ferox also are cultivated or harvested from the wild for similar applications.
The genus is native to Africa; species are found in southern Africa, the mountains of tropical Africa, various islands off the coast of Africa including Madagascar, and the Arabian Peninsula.
The APG III system (2009) places the genus in the family Xanthorrhoeaceae, subfamily Asphodeloideae. In the past it has also been assigned to families Aloaceae and Liliaceae or lily family. The plant Agave americana, which is sometimes called "American aloe", belongs to the Asparagaceae, a different family.
Most Aloe species have a rosette of large, thick, fleshy leaves. The rosette may appear to be stemless or may be borne on a branched or unbranched stem; some species native to South Africa are treelike. Aloe flowers are tubular, frequently yellow, orange, pink or red, and are borne, densely clustered and pendant, at the apex of simple or branched, leafless stems.
Most Aloe species have a rosette of large, thick, fleshy leaves. The leaves are often lance-shaped with a sharp apex and a spiny margin. Aloe flowers are tubular, frequently yellow, orange, pink or red, and are borne, densely clustered and pendant, at the apex of simple or branched, leafless stems. Many species of Aloe appear to be stemless, with the rosette growing directly at ground level; other varieties may have a branched or unbranched stem from which the fleshy leaves spring. They vary in color from grey to bright-green and are sometimes striped or mottled. Some Aloes native to South Africa are arborescent.
The APG III system (2009) places the genus in the family Xanthorrhoeaceae, subfamily Asphodeloideae. In the past it has also been assigned to the families Liliaceae and Aloeaceae, as well as the family Asphodelaceae, before this was merged into the Xanthorrhoeaceae.
The circumscription of the genus has varied widely. Many genera, such as Lomatophyllum, have been brought into synonymy. Species at one time placed in Aloe, such as Agave americana, have been moved to other genera.
There are over 500 accepted species in the genus Aloe, plus even more synonyms and unresolved species, not to mention subspecies, varieties and hybrids. Some of the accepted species are:
- Aloe aculeata Pole-Evans
- Aloe africana Mill.
- Aloe albida (Stapf) Reynolds
- Aloe albiflora Guillaumin
- Aloe arborescens Mill.
- Aloe arenicola Reynolds
- Aloe argenticauda Merxm. & Giess
- Aloe aristata Haw.
- Aloe bakeri Scott-Elliot
- Aloe ballii Reynolds
- Aloe ballyi Reynolds
- Aloe barberae Dyer
- Aloe brevifolia Mill.
- Aloe broomii Schönland
- Aloe buettneri A.Berger
- Aloe camperi Schweinf.
- Aloe capitata Baker
- Aloe ciliaris Haw.
- Aloe commixta A.Berger
- Aloe comosa Marloth & A.Berger
- Aloe corallina Verd.
- Aloe decumbens (Reynolds) van Jaarsv.
- Aloe dewinteri Giess ex Borman & Hardy
- Aloe dichotoma Masson
- Aloe dinteri A.Berger
- Aloe eminens Reynolds & Bally
- Aloe erinacea D.S.Hardy
- Aloe excelsa A.Berger
- Aloe ferox Mill.
- Aloe forbesii Balf.f.
- Aloe gracilis Haw.
- Aloe haemanthifolia Marloth & A.Berger
- Aloe helenae Danguy
- Aloe hereroensis Engl.
- Aloe inermis Forssk.
- Aloe inyangensis Christian
- Aloe jawiyon S.J.Christie, D.P.Hannon & Oakman ex A.G.Mill.
- Aloe jucunda Reynolds
- Aloe juddii van Jaarsv.
- Aloe khamiesensis Pillans
- Aloe kilifiensis Christian
- Aloe maculata All.
- Aloe marlothii A.Berger
- Aloe namibensis Giess
- Aloe nyeriensis Christian & I.Verd.
- Aloe pearsonii Schönland
- Aloe peglerae Schönland
- Aloe perfoliata L.
- Aloe perryi Baker
- Aloe petricola Pole-Evans
- Aloe pillansii L.Guthrie
- Aloe plicatilis (L.) Mill.
- Aloe polyphylla Pillans
- Aloe ramosissima Pillans
- Aloe rauhii Reynolds
- Aloe reynoldsii Letty
- Aloe scobinifolia Reynolds & Bally
- Aloe sinkatana Reynolds
- Aloe sladeniana Pole-Evans
- Aloe squarrosa Baker ex Balf.f.
- Aloe striata Haw.
- Aloe striatula Haw.
- Aloe succotrina Lam.
- Aloe suzannae Decary
- Aloe tenuior Haw.
- Aloe thraskii Baker
- Aloe variegata L.
- Aloe vera (L.) Burm.f.
- Aloe viridiflora Reynolds
- Aloe wildii (Reynolds) Reynolds
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Aloe species are frequently cultivated as ornamental plants both in gardens and in pots. Many aloe species are highly decorative and are valued by collectors of succulents. Aloe vera is used both internally and externally on humans, and is claimed to have some medicinal effects, which have been supported by scientific and medical research. They can also be made into types of special soaps.
Historical uses 
Of the 500+ species, only a few were used traditionally as a herbal medicine, Aloe vera again being the most commonly used species. Also included are A. perryi and A. ferox. The Ancient Greeks and Romans used Aloe vera to treat wounds. In the Middle Ages, the yellowish liquid found inside the leaves was favored as a purgative. Unprocessed aloe that contains aloin is generally used as a laxative, whereas processed Aloe vera juice does not usually contain significant aloin.
Some species, particularly Aloe vera, are used in alternative medicine and first aid. Both the translucent inner pulp and the resinous yellow aloin from wounding the aloe plant are used externally to relieve skin discomforts. As an herbal medicine, Aloe vera juice is commonly used internally to relieve digestive discomfort.
There have been relatively few studies about possible benefits of aloe gel taken internally. Components of Aloe have shown the possibility of inhibiting tumor growth in animal studies, but these effects have not been demonstrated clinically in humans. There have been some studies in animal models which indicate that extracts of Aloe have a significant anti-hyperglycemic effect, and may be useful in treating Type II diabetes, but these studies have not been confirmed in humans.
Aloin in OTC laxative products 
On May 9, 2002, the U.S. Food and Drug Administration issued a final rule banning the use of aloin, the yellow sap of the aloe plant for use as a laxative ingredient in over-the-counter drug products. Most aloe juices today do not contain significant aloin.
Chemical properties 
According to W. A. Shenstone, two classes of aloins are to be recognized: (1) nataloins, which yield picric and oxalic acids with nitric acid, and do not give a red coloration with nitric acid; and (2) barbaloins, which yield aloetic acid (C7H2N3O5), chrysammic acid (C7H2N2O6), picric and oxalic acids with nitric acid, being reddened by the acid. This second group may be divided into a-barbaloins, obtained from Barbados Aloe, and reddened in the cold, and b-barbaloins, obtained from Socotrine and Zanzibar Aloe, reddened by ordinary nitric acid only when warmed or by fuming acid in the cold. Nataloin (2C17H13O7·H2O) forms bright yellow scales, barbaloin (C17H18O7) prismatic crystals. Aloe species also contain a trace of volatile oil, to which its odour is due.
See also 
- "Aloe Vera: Science and Safety". NIH National Center for Complementary and Alternative Medicine. April 2012. Retrieved 31 March 2013.
- Stevens, P.F. (2001 onwards). "Angiosperm Phylogeny Website: Asparagales: Asphodeloideae".
- Rodd, Tony; Stackhouse, Jennifer (2008). Trees: a Visual Guide. Berkeley: University of California Press. p. 131. ISBN 9780520256507.
- "Aloe". World Checklist of Selected Plant Families. Royal Botanic Gardens, Kew. Retrieved 2013-02-25.
- "Lomatophyllum". World Checklist of Selected Plant Families. Royal Botanic Gardens, Kew. Retrieved 2013-02-25.
- "Aloe americana". World Checklist of Selected Plant Families. Royal Botanic Gardens, Kew. Retrieved 2013-02-25.
- The Plant List (2010). Version 1. Published on the Internet; http://www.theplantlist.org/ (accessed December 2012)
- Tom Reynolds, ed. (2004). Aloes: the Genus Aloe. Boca Raton: CRC Press. ISBN 978-0-415-30672-0.
- Wong, Cathy (September 15, 2012). "Heartburn Remedies". About.com.
- "Aloe IBS study".
- Cosmetic Ingredient Review Expert, Panel (2007). "Final report on the safety assessment of Aloe andongensis extract, Aloe andongensis leaf juice, Aloe arborescens leaf extract, Aloe arborescens leaf juice, Aloe arborescens leaf protoplasts, Aloe barbadensis flower extract, Aloe barbadensis leaf, Aloe barbadensis leaf extract, Aloe barbadensis leaf juice, Aloe barbadensis leaf polysaccharides, Aloe barbadensis leaf water, Aloe ferox leaf extract, Aloe ferox leaf juice, and Aloe ferox leaf juice extract". Int. J. Toxicol. 26 (Suppl 2): 1–50. doi:10.1080/10915810701351186. PMID 17613130.
- Tanaka M, Misawa E, Ito Y, Habara N, Nomaguchi K, Yamada M, Toida T, Hayasawa H, Takase M, Inagaki M, Higuchi R (2006). "Identification of five phytosterols from Aloe vera gel as anti-diabetic compounds". Biol. Pharm. Bull. 29 (7): 1418–22. doi:10.1248/bpb.29.1418. PMID 16819181.
- "Status of certain additional over-the-counter drug category II and III active ingredients. Final rule". Fed Regist (Food and Drug Administration, HHS) 67 (90): 31125–7. 2002. PMID 12001972.
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