Aloe vera

Aloe vera
A. vera growing in Aruba, flower detail inset.
Scientific classification
Kingdom: Plantae (unranked): Angiosperms (unranked): Monocots Order: Asparagales Family: Asphodelaceae Genus: Aloe Species: A. vera
Binomial name
Aloe vera (L.) Burm.f.

Aloe vera, also known as the Medicinal Aloe, is a species of succulent plant that probably originated in northern Africa. The species does not have any naturally occurring populations, although closely related Aloes do occur in northern Africa.^[1] The species is frequently cited as being used in herbal medicine since the beginning of the first century AD, because it is mentioned in the New Testament (John 19:39–40 And there came also Nicodemus, which at the first came to Jesus by night, and brought a mixture of myrrh and aloes... ).^[2] However, it is unclear whether the aloes described in the Bible are derived from A. vera. Extracts from A. vera are widely used in the cosmetics and alternative medicine industries, being marketed as variously having rejuvenating, healing or soothing properties.^[3][4][5] There is, however, little scientific evidence of the effectiveness or safety of A. vera extracts for either cosmetic or medicinal purposes, and what positive evidence is available is frequently contradicted by other studies.^[6][7][8][9] Despite these limitations, there is some preliminary evidence that A. vera extracts may be useful in the treatment of diabetes and elevated blood lipids in humans.^[8] These positive effects are thought to be due to the presence of compounds such as mannans, anthraquinones and lectins.^[8][10][11]

Description

Spotted forms of A. vera are sometimes known as A. vera var. chinensis

A. vera is a stemless or very short-stemmed succulent plant growing to 60–100 cm (24–39 in) tall, spreading by offsets. The leaves are lanceolate, thick and fleshy, green to grey-green, with some varieties showing white flecks on the upper and lower leaf surfaces.^[12] The margin of the leaf is serrated and has small white teeth. The flowers are produced in summer on a spike up to 90 cm (35 in) tall, each flower pendulous, with a yellow tubular corolla 2–3 cm (0.8–1.2 in) long.^[12][13] Like other Aloe species, A. vera forms arbuscular mycorrhiza, a symbiosis that allows the plant better access to mineral nutrients in soil.^[14]

Taxonomy and etymology

The species has a number of synonyms: A. barbadensis Mill., Aloe indica Royle, Aloe perfoliata L. var. vera and A. vulgaris Lam.,^[15][16] and common names including Chinese Aloe, Indian Aloe, True Aloe, Barbados Aloe, Burn Aloe, First Aid Plant, Wand of Heaven and Miracle Plant.^{[13][17][18][19][20]} The species name vera means true or genuine.^[17] Some literature identifies the white spotted form of A. vera as A. vera var. chinensis,^[21][22] however, the species varies widely with regard to leaf spots^[1] and it has been suggested that the spotted form of A. vera may be conspecific with A. massawana.^[23] The species was first described by Carl Linnaeus in 1753 as Aloe perfoliata var. vera,^[24] and was described again, twice, in 1768 by Nicolaas Laurens Burman and Philip Miller. Burman described the species as Aloe vera in Flora Indica on the 6th of April, 1768 while Miller described the species as Aloe barbadensis some ten days later in the Gardener's Dictionary.^[25]

Techniques based on DNA comparison suggest that A. vera is relatively closely related to Aloe perryi, a species that is endemic to Yemen.^[26] Similar techniques, using chloroplast DNA sequence comparison and ISSR profiling have also suggested that A. vera is closely related to Aloe forbesii, Aloe inermis, Aloe scobinifolia, Aloe sinkatana and Aloe striata.^[27] With the exception of South African species, A. striata, these Aloe species are native to Socotra (Yemen), Somalia and Sudan.^[27] The lack of obvious natural populations of the species have led some authors to suggest that A. vera may be of hybrid origin.^[28]

Distribution

The natural range of A. vera is unclear, as the species has been widely cultivated throughout the world. It has been suggested that naturalised stands of the species occur through North Africa in Algeria, Morocco, and Tunisia, along with the Canary and Madeira Islands.^[15] The species was introduced to China, India, Pakistan and various parts of southern Europe in the 17th century.^[29] The species is widely naturalised elsewhere, occurring in temperate and tropical regions of Australia, Barbados, Belize, Nigeria, Paraguay and the USA.^[1][30] It has been suggested that, like many Aloes, the species is originally from Southern Africa and that populations that occur elsewhere are the result of human cultivation.^[1]

Cultivation

Aloe vera growing as an ornamental plant

A. vera has been widely grown as an ornamental plant. The species is popular with modern gardeners as a putatively medicinal plant and due to its interesting flowers, form and succulence. This succulence enables the species to survive in areas of low natural rainfall, making it ideal for rockeries and other low-water use gardens.^[12] The species is hardy in zones 8–11, although it is intolerant of very heavy frost or snow.^[13][31] The species is relatively resistant to most insect pests, though mealy bugs, scale insects and aphid species may cause a decline in plant health.^[32][33] In pots, the species requires well-drained sandy potting soil and bright sunny conditions. The use of a good quality commercial propagation mix or pre-packaged "cacti and succulent mixes" are recommended as they allow good drainage.^[34] Terracotta pots are preferable as they are porous.^[34] Potted plants should be allowed to completely dry prior to re-watering. During winter, A. vera may become dormant, during which little moisture is required. In areas that receive frost or snow the species is best kept indoors or in heated glasshouses.^[13] Large scale agricultural production of A. vera is undertaken in Australia,^[35] Cuba,^[36] the Dominican Republic, Mexico,^[37] India,^[38] Jamaica,^[39] Kenya and South Africa,^[40] along with the USA^[41] to supply the cosmetics industry with A. vera gel.

Anthropogenic uses

Moisturizer containing A. vera

Scientific evidence for the cosmetic and therapeutic effectiveness of Aloe vera is limited and when present is typically contradictory.^[6][7] Despite this, the cosmetic and alternative medicine industries regularly make claims regarding the soothing, moisturising and healing properties of A. vera, especially via Internet advertising.^[3][4][5][8] As a food, A. vera is very bitter and unpalatable.^[42] A. vera gel, however, is used as an ingredient in commercially available yogurt, beverages and some desserts.^[43][44][45] It is common practice for cosmetic companies to add sap or other derivatives from A. vera to products such as makeup, tissues, moisturizers, soaps, sunscreens, incense, razors and shampoos.^[43] It has also been suggested that biofuels could be obtained from A. vera seeds.^[46] Other uses for extracts of A. vera include the dilution of semen for the artificial fertilisation of sheep,^[47] use as fresh food preservative,^[48] and use in water conservation in small farms.^[49]

Medicine

Aloe vera has a long association with herbal medicine, although it is not known when its medical applications were first discovered. Early records of A. vera use appear in the Ebers Papyrus from 16th century BCE,^[20] in both Dioscorides' De Materia Medica and Pliny the Elder's Natural History written in the mid-first century CE^[20] along with the Juliana Anicia Codex produced in 512 CE.^[43] Contrary to the widespread belief that A. vera is non-toxic, excess ingestion of A. vera has been associated with a range of symptoms and conditions including diarrhea, hepatitis, kidney dysfunction, electrolyte imbalance and reduced CNS activity.^[8][9][50] However, the species is used widely in the traditional herbal medicine of China, Japan and India.^[8]

A. vera yoghurt

Aloe vera is alleged to be effective in treatment of wounds.^[9] Evidence on the effects of A. vera sap on wound healing, however, is limited and contradictory.^[9] Some studies, for example, show that A. vera promotes the rates of healing,^[51][52] while in contrast, other studies show that the healing time of wounds to which Aloe vera gel was applied were significantly slower to heal.^[53][54] In addition to topical use in wound or burn healing, internal intake of A. vera has been linked with improved blood glucose levels in diabetics,^[55][56] and with lower blood lipids in hyperlipidaemic patients.^[57] In other diseases, preliminary studies have suggested oral A. vera gel may reduce symptoms and inflammation in patients with ulcerative colitis.^[58] Compounds extracted from A. vera have been used as an immunostimulant that aids in fighting cancers in cats and dogs;^[10] however, this treatment has not been scientifically tested in humans. The injection of A. vera extracts to treat cancer has resulted in the deaths of several patients.^[59]

A. vera extracts have antibacterial and antifungal activities. For example, A. vera extracts have been shown to inhibit the growth of fungi that cause tinea,^[60] however, evidence for control beneath human skin remains to be established. For bacteria, inner-leaf gel from A. vera was shown to inhibit growth of Streptococcus and Shigella species in vitro.^[61] In contrast, A. vera extracts failed to show antibiotic properties against Xanthomonas species.^[62]

Biologically active compounds

A. vera leaves contain a range of biologically active compounds, the best studied being acetylated mannans, polymannans, anthraquinone C-glycosides, anthrones and anthraquinones and various lectins.^[8][10][11]

See also

• Aloe
• Asphodelaceae
• Herbal medicine
• Succulent plants
• Medicinal plants

References

External links

• Aloe vera monograph
• Aloe vera at the Open Directory Project
• The International Aloe Science Council