Aloe emodin.svg

''Aloe'' (; also written ''Aloë'') is a genus containing over 650 species of flowering succulent plants.WFO (2022): Aloe L. Published on the Internet;http://www.worldfloraonline.org/taxon/wfo-4000001341. Accessed on: 06 Nov 2022 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.Stevens, P.F. (2001 onwards).
Asphodelaceae
. ''Angiosperm Phylogeny Website''. Retrieved 2016-06-09. 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.).

Taxonomy

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'').

Uses

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 as folk or alternative medicine. The ''Aloe'' species is known for its medicinal and cosmetic properties. Around 75% of ''Aloe'' species are used locally for medicinal uses. The plants can also be made into types of special soaps or used in other skin care products (see natural skin care).

Numerous cultivars with mixed or uncertain parentage are grown. Of these, ''Aloe'' ‘Lizard Lips’ has gained the Royal Horticultural Society’s Award of Garden Merit.

''Aloe variegata'' has been planted on graves in the superstitious belief that this ensures eternal life.

Historical uses

Historical use of various aloe species is well documented. Documentation of the clinical effectiveness is available, although relatively limited.

Of the 500+ species, only a few were used traditionally as herbal medicines, ''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 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 for skin discomforts. As an herbal medicine, ''Aloe vera'' juice is commonly used internally for digestive discomfort.

According to Cancer Research UK, a potentially deadly product called T-UP is made of concentrated aloe, and promoted as a cancer cure. They say "there is currently no evidence that aloe products can help to prevent or treat cancer in humans".

Aloin in OTC laxative products

On May 9, 2002, the US 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 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 ''Aloe Socotrina'' 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 are used in essential oils as a safety measure to dilute the solution before they are applied to the skin.

Flavoring

''Aloe perryi'', ''A. barbadensis'', ''A. ferox'', and hybrids of this species with ''A. africana'' and ''A. spicata'' are listed as natural flavoring substances in the US government ''Electronic Code of Federal Regulations''. ''Aloe socotrina'' is said to be used in yellow Chartreuse.John Tellman (1900
''The Practical Hotel Steward''
The Hotel Monthly, Chicago

Heraldic occurrence

''Aloe rubrolutea'' occurs as a charge in heraldry, for example in the Civic Heraldry of Namibia.

Gallery

File:Aloe vossii - plant (aka).jpg, ''Aloe vossii''
File:Aloe rubroviolacea2.jpg, '' A. rubroviolacea''
File:Aloe africana 1.jpg, ''Aloe africana'' (Uitenhage aloe)
File:Gardenology-IMG 5394 hunt10mar.jpg, ''Aloe marlothii'' (flat-flowered aloe)
File:Aloe pluridens (3).jpg, ''Aloe pluridens'' (French aloe)
File:Aloe excelsa at Mount Coot-tha.JPG, ''Aloe excelsa'' (Zimbabwe aloe)
File:Aloe rupestris, vroeë bloeiwyse, Pretoria.jpg, ''Aloe rupestris'' (bottlebrush aloe)
File:Aloe speciosa - tilt head aloe.jpg, ''Aloe hexapetala'' (tilt-headed aloe)
File:Blooming aloes wide view alternate, with bright sun behind.jpg, Blooming ''Aloe arborescens''
File:Aloe cooperi in flower IMG 1702e.JPG, ''Aloe cooperi'' (''Aloe plicatilis'' in background on the right)
File:Aloe hereroensis Auob C15.JPG, ''Aloe hereroensis''
File:Aloe peglerae01.jpg, ''Aloe peglerae''
File:Aloe saponaria 1.jpg, ''Aloe maculata'' - prev. ''A. saponaria'' (soap aloe)
File:Aloe reitzii flowers.jpg, ''Aloe reitzii''

See also

* List of ''Aloe'' species
* List of ineffective cancer treatments
* List of Southern African indigenous trees

References

Further reading

*
*

External links

{{Authority control

Plants used in Ayurveda
Asphodelaceae genera
Laxatives
Cosmetics chemicals
Succulent plants