Aloe (; also written Aloë) 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.
The APG IV system (2016) places the genus in the family Asphodelaceae, subfamily Asphodeloideae. Within the subfamily it may be placed in the tribe Aloeae. In the past, it has been assigned to the family Aloaceae (now included in the Asphodeloidae) or to a broadly circumscribed family Liliaceae (the lily family). The plant Agave americana, which is sometimes called "American aloe", belongs to the Asparagaceae, a different family.
The genus is native to tropical and southern Africa, Madagascar, Jordan, the Arabian Peninsula, and various islands in the Indian Ocean (Mauritius, Réunion, Comoros, etc.). A few species have also become naturalized in other regions (Mediterranean, India, Australia, North and South America, Hawaiian Islands, etc.).
Etymology
The genus name Aloe is derived from the Arabic word alloeh, meaning "bitter and shiny substance" or from Hebrew ahalim, plural of ahal.
Description
Most Aloe species have a rosette of large, thick, fleshy leaves. 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 tree-like (arborescent).
Systematics
The APG IV system (2016) places the genus in the family Asphodelaceae, subfamily Asphodeloideae. In the past it has also been assigned to the families Liliaceae and Aloeaceae, as well as the family Asphodelaceae sensu stricto, before this was merged into the Asphodelaceae sensu lato.
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. Molecular phylogenetic studies, particularly from 2010 onwards, suggested that as then circumscribed, Aloe was not monophyletic and should be divided into more tightly defined genera. In 2014, John Charles Manning and coworkers produced a phylogeny in which Aloe was divided into six genera: Aloidendron, Kumara, Aloiampelos, Aloe, Aristaloe and Gonialoe.
Species
Over 600 species are accepted in the genus Aloe, plus even more synonyms and unresolved species, 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 bakeri Scott-Elliot Aloe ballii Reynolds Aloe ballyi Reynolds Aloe brevifolia Mill. Aloe broomii Schönland Aloe buettneri A.Berger Aloe camperi Schweinf. Aloe capitata Baker Aloe comosa Marloth & A.Berger Aloe cooperi Baker Aloe corallina Verd. Aloe dewinteri Giess ex Borman & Hardy Aloe erinacea D.S.Hardy Aloe excelsa A.Berger Aloe ferox Mill. Aloe forbesii Balf.f. 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 khamiesensis Pillans Aloe kilifiensis Christian Aloe maculata All. Aloe marlothii A.Berger Aloe mubendiensis Christian 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 polyphylla Pillans Aloe rauhii Reynolds Aloe reynoldsii Letty Aloe scobinifolia Reynolds & Bally Aloe sinkatana Reynolds Aloe squarrosa Baker ex Balf.f. Aloe striata Haw. Aloe succotrina Lam. Aloe suzannae Decary Aloe thraskii Baker Aloe vera (L.) Burm.f. Aloe viridiflora Reynolds Aloe wildii (Reynolds) Reynolds
In addition to the species and hybrids between species within the genus, several hybrids with other genera have been created in cultivation, such as between Aloe and Gasteria (× Gasteraloe), and between Aloe and Astroloba (×Aloloba).