There are about 400 species of aloe. Most aloe plants have thick, fleshy leaves edged with spines. Their flowers are often shades of red, pink, yellow, or orange. Many people grow aloe plants in homes or gardens. Aloe vera is the best-known species of aloe, and it is found in many products. For example, gel from the leaves is used to treat burns.
Molecular Biology and Genetics
Statistics of barcoding coverage
Specimens with Sequences:399
Specimens with Barcodes:366
Species With Barcodes:117
Aloe ser. Macrifoliae
Aloe ser. Macrifoliae (the "Climbing Aloes") is a taxonomic series within the genus Aloe, comprising seven closely related species of Southern African climbing aloe. These aloes are typically multi-branched climbing or sprawling shrubs, with long spindly stems and a large woody base on the ground. These characteristics, as well as their soft, narrow, triangular leaves whose lower part ensheathes the stem, make these Aloes easy to distinguish.
This group of aloes is centered in the Eastern Cape, South Africa where they are also particularly common. A few rare species also occur in isolated pockets further west in the fynbos vegetation of the Western Cape.
The most common species in this group is probably Aloe ciliaris which is relatively widespread in South Africa. It seems to have developed from the smaller, rarer, finely leaved Aloe tidmarshi (now re-classified as a subspecies, Aloe ciliaris tidmarshi) and to have spread out across the country relatively recently.
Its relatives, moving westwards along the South African coast, are: Aloe tenuior of Kwazulu-Natal and the Eastern Cape, Aloe striatula of the higher mountain ranges bordering the Karoo, and Aloe gracilis of the area around Port Elizabeth (where the Eastern Cape thickets fade into the Western Cape fynbos vegetation).
Further west, the Fynbos vegetation of the neighbouring Western Cape is subject to frequent fires, making it relatively inhospitable for Aloes. Nevertheless, several rare relict Macrifoliae Aloe species survive in tiny isolated pockets within the Fynbos biome, such as Aloe decumbens, Aloe juddii and Aloe commixta.
The unusual and endangered Pearson's Aloe (Aloe pearsonii) of Namibia is considered by many botanists to be an outlying member of this series. However more recent chemical analysis indicates that it is actually closer to the "Creeping Aloes" (Mitriformes), but is most likely a "missing-link" intermediate between the two groups. 
The different species of this series show clear and distinct adaptations to their different natural habitats. The climbing aloe species that are indigenous to regions with tall, thicket vegetation are tall and erect - often with hooked, recurved leaves that allow the aloes to anchor their branches and climb up through trees and thickets. In contrast, the species from drier regions with low, sparse, fynbos vegetation tend to be more "decumbent", rambling along the ground - with no need for their leaves to be recurved. 
Species and subspecies
- Aloe ciliaris comprising:
- A. ciliaris var. ciliaris
- A. ciliaris var. tidmarshii
- A. ciliaris var. redacta
- Aloe striatula comprising:
- A. striatula var. striatula
- A. striatula var. caesia
- Aloe tenuior comprising:
- A. tenuior var. tenuior
- A. tenuior var. glaucescens
- A. tenuior var. densiflora
- A. tenuior var. decidua
- A. tenuior var. viridifolia
- A. tenuior var. rubriflora
- Aloe gracilis comprising:
- A. gracilis var. gracilis
- A. gracilis var. laxiflora
- A. gracilis var. decumbens (upgraded to species, van Jaarsveld 2008)
- Aloe decumbens of the Langeberg Mountains, Western Cape.
- Aloe juddii of the Koudeberg Mountains, Western Cape.
- Aloe commixta of Table Mountain, Western Cape.
Due to their hardiness and the wide range of flower colours, these slender aloes have become popular ornamental plants in South African gardens. The commoner species (such as the more widespread aloes of the Eastern Cape) are increasingly grown in gardens overseas too. Like most aloes, Climbing Aloes require a sunny, well-drained position and are particularly suitable for rockeries. The taller, climbing species are commonly planted along fences and boundaries where they grow up through the surrounding foliage. The lower, rambling species however, are better suited for rockeries, slopes or terraces, which they will naturally cascade down over.
The colour of the flowers varies from bright yellow (Aloe commixta and Aloe tenuior) to orange (Aloe striatula and Aloe commixta) to red, pink or even scarlet (Aloe ciliaris, Aloe juddii and Aloe gracilis). There can also be significant colour variation among different populations within each individual species.
They can easily be propagated by taking cuttings (truncheons), as well as by seed. These aloes generally have both male and female flowers on each plant, but an individual plant is usually not self-fertile by itself. However, some of the different Macrifoliae aloe species are also inter-fertile, and can thus form hybrids.
- Court D: Succulent Flora of Southern Africa. Cape Town: Struik Nature. 2010. ISBN 978-1-77007-587-0
- Reynolds, G: The Aloes of South Africa. Cape Town: A.A.Balkema 1969.
The genus is native to Africa, and is common in South Africa's Cape Province, the mountains of tropical Africa, and neighboring areas such as Madagascar, the Arabian peninsula, and the islands of Africa.
The APG III system (2009) places the genus in the family family Xanthorrhoeaceae, subfamily Asphodeloideae. In the past it has also been assigned to families Aloaceae and Liliaceae or lily family. Members of the closely allied genera Gasteria, Haworthia and Kniphofia, which have a similar mode of growth, are also popularly known as aloes. Note that the plant sometimes called American aloe (Agave americana) belongs to Agavaceae, a different family.
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.
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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. The gel in the leaves can be made into a smooth type of cream that can heal burns such as sunburn. They can also be made into types of special soaps.
Of the 299 species of Aloe, only a few were used traditionally as a herbal medicine, aloe vera again being the most commonly used version of aloe in herbal medicine. Also included are Aloe perryi (found in northeastern Africa) and Aloe ferox (found in South Africa). The 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. Processed 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 in the home first aids. 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 "aloe for heartburn". Better Nutrition. 2007. http://findarticles.com/p/articles/mi_m0FKA/is_4_69/ai_n18791510. "aloe alt med". http://altmedicine.about.com/od/therapiesfrometol/a/heartburn.htm. "Aloe IBS study". http://www.medscape.com/viewarticle/546327. . Some modern research suggests Aloe vera can significantly slow wound healing compared to normal protocols of treatment. Other reviews of randomised and controlled clinical trials have provided no evidence that Aloe vera has a strong medicinal effect.
Today, aloe vera is used both internally and externally on humans. The gel found in the leaves is used for soothing minor burns, wounds, and various skin conditions like eczema and ringworm. The extracted aloe vera juice aloe vera plant is used internally to treat a variety of digestive conditions. The use of this herbal medicine was popularized in the 1950s in many Western countries. The gel's effect is nearly immediate; it also applies a layer over wounds that is said to reduce the chance of any infection.
There have been relatively few studies about possible benefits of Aloe gel taken internally. Components of Aloe may inhibit tumor growth. 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. 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.
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 hi 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.
There are around 400 species in the genus Aloe. For a full list, see List of species of genus Aloe. Species include:
- Aloe vera - used in healthcare & health products
- Aloe arborescens - used in healthcare
- Aloe aristata - Torch Plant, Lace Aloe dichotoma - quiver tree or kokerboom
- Aloe nyeriensis
- Aloe variegata - Partridge-breasted Aloe, Tiger Aloe barbadensis - Barbados Aloe, Common Aloe, Yellow Aloe, Medicinal Aloe. This is an older name for Aloe vera.
- Aloe wildii
- ^ Stevens, P.F. (2001 onwards), Angiosperm Phylogeny Website: Asparagales: Asphodeloideae, http://www.mobot.org/MOBOT/Research/APweb/orders/asparagalesweb.htm#Asphodelaceae
- ^ Images of aloe trees.
- ^ Reynolds, T (ed) Aloes: The genus Aloe. CRC Press. ISBN 978-0-415-30672-0
- ^ Schmidt JM, Greenspoon JS (1991). "Aloe vera dermal wound gel is associated with a delay in wound healing". Obstet Gynecol 78 (1): 115–7. PMID 2047051.
- ^ Richardson J, Smith JE, McIntyre M, Thomas R, Pilkington K (2005). "Aloe vera for preventing radiation-induced skin reactions: a systematic literature review". Clin Oncol (R Coll Radiol) 17 (6): 478–84. PMID 16149293.
- ^ Ernst E, Pittler MH, Stevinson C (2002). "Complementary/alternative medicine in dermatology: evidence-assessed efficacy of two diseases and two treatments". Am J Clin Dermatol 3 (5): 341–8. doi:10.2165/00128071-200203050-00006. PMID 12069640.
- ^ 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.
- ^ Food And Drug Administration,, HHS (2002). "Status of certain additional over-the-counter drug category II and III active ingredients. Final rule". Fed Regist 67 (90): 31125–7. PMID 12001972.
- ^ "NAMIBIA - WINDHOEK". http://www.ngw.nl/int/afr/windhoek.htm. Retrieved 2008-01-24.
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