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Aloe arborescens Mill.

Protologue
Gard. dict. ed. 8: Aloe n.3 (1768).
Family
Asphodelaceae
Chromosome number
2n = 14
Vernacular names
Krantz aloe, Kidachi aloe, mountain bush aloe, candelabra aloe, octopus plant, torch plant (En). Aloès arborescent (Fr).
Origin and geographic distribution
Aloe arborescens is native to southern Africa and occurs in Malawi, Botswana, Zimbabwe and Mozambique as well as South Africa. It has been imported in many countries in the tropics and subtropics as an ornamental and medicinal plant. In Italy it is commercially grown for its medicinal and cosmetic uses and in Japan for both medicine and food. In Japan, where it was first introduced in the 17th century, it has become naturalized. Commercial growing of Aloe arborescens has started recently in Israel and China.
Uses
The split or crushed fresh leaves of Aloe arborescens are widely used to treat burns and wounds. In South Africa a leaf decoction is given to women to ease childbirth. In Japan the leaves are used as a vegetable and as a health food because they are thought to overcome constipation. Parts of the stem with a number of leaves attached are marketed as a vegetable. Preparations are sold as over-the-counter drugs for acceleration of gastric secretion, as a purgative and for dermatological use. Aloe arborescens is an important ingredient of ‘Kidachi aloe candies’ popular in Japan for their tangy yoghurt flavour. Worldwide attention was drawn to the possible value of gel prepared from Aloe arborescens after the second World War, when skin burns of victims of the nuclear bombs on Japan were successfully treated with this gel. In southern Africa Aloe arborescens is planted as a living fence. Homesteads that have been abandoned for over a century can still be traced thanks to surviving fences. Aloe arborescens is grown widely as an ornamental in the subtropics and is especially popular in the Mediterranean region.
Production and international trade
There are no statistics available on the production of Aloe arborescens. Japan is probably the largest producer, but for the national market only.
Properties
As in most Aloe species, the leaf exudate of Aloe arborescens contains anthrone 10-C-glucosides (anthraquinone derivatives) such as aloin and hydroxyaloins. Aloin is a mixture of the stereoisomers aloin A (barbaloin) and aloin B (isobarbaloin). Furthermore, the exudate contains the pyrone derivative aloenin and free and glucosylated 2-acetonyl-7- hydroxy-5-methylchromones (e.g. aloesone, furoaloesone, aloeresin A, aloeresin B (aloesin) and aloeresin C). The compound responsible for the laxative properties is aloin, which itself is inactive as a laxative, but is activated by Eubacterium sp. to aloe-emodin anthrone. Although some observations indicate that in diarrhoea induced by aloin, increased water content might be more important than stimulated peristalsis, the side effects of prolonged use point to a griping effect on the colon. Anthraquinone laxatives should not be used for longer than 8–10 days, or by children younger than 12 years. Contra-indications include pregnancy, breastfeeding, intestinal inflammations and haemorrhoids. It has been claimed that aloin is responsible for antihistamine and anti-inflammatory activity. Aloin should be administered preferably in combination with an antispasmodic to moderate its griping action. Possible side effects of aloin include congestion and irritation of the pelvic organs. Anthraquinone laxatives may play a role in development of colorectal cancer as they have genotoxic potential and also tumorigenic potential in rodents. Both aloin and aloeresin B have skin-whitening activity. In 2002 the United States Food and Drug Administration withdrew the ‘generally recognized as safe and effective (GRASE)’ status for over-the-counter drugs based on aloe exudates.
The gel contains polysaccharides and glycoproteins. Apart from mannan and glucomannan, arboran A and arboran B have been identified, which have hypoglycaemic effects. The structure–function relationship of polysaccharides from gel from different Aloe species is still subject to research. Biological activity is thought to be, at least partly, due to immunomodulating effects of these polysaccharides.
The leaf epidermis contains lectins (aloctin A and aloctin B) that inhibit the growth of fibrosarcoma in animals. Aloe arborescens leaf powder showed protective effects on mouse skin injury induced by soft X-irradiation. It also showed protective effects against human carcinogenesis. Aloe arborescens gel works as a synergist of neomycin sulfate in eye drops; they are useful in the treatment of inflammation and infections of the eye.
Freeze-dried leaves have shown a 70% growth inhibition of Trichophyton mentagrophytes (one of the fungi causing athlete’s foot in humans), induced in guinea-pigs feet in vivo.
Adulterations and substitutes
Psyllium (Plantago spp.), which is a natural bulk laxative, is one of the substitutes for anthraquinone-containing laxative drugs such as aloe that may cause dependency and/or cathartic colon. Anthraquinone-containing preparations from Senna alata (L.) Roxb. and other Senna and Cassia species are sometimes recommended as substitutes for Aloe products. Centella asiatica (L.) Urb. is recommended as a substitute for Aloe vera gels in wound treatments; its triterpenes have exhibited both wound healing and antibacterial activities.
Description
Succulent shrub up to 5 m tall; stems solitary, branching at or near the base, with persistent dead leaves. Leaves in a dense rosette, spreading, becoming recurved; stipules absent; petiole absent; blade lanceolate, up to 60 cm × 7 cm, apex long-acuminate, margin with firm, deltoid, forward-pointing, yellow teeth, c. 4 mm long, 1–1.5 cm apart, blade greyish green, reddish tinged in dry conditions. Inflorescence a terminal raceme, 20–40 cm long, 1–4 per rosette, erect, cylindrical-acuminate, very densely flowered; peduncle up to 60 cm long, simple or rarely with 1 short branch; bracts broadly ovate, 2–5 mm long. Flowers bisexual, regular, 3-merous; pedicel 1–1.5 cm long; perianth tubular, 3.5–4 cm long, c. 7 mm in diameter, lobes 6, free to the base, bright orange to scarlet; stamens 6, exserted; ovary superior, 3-celled, style filiform, stigma head-shaped, exserted. Fruit an oblong-ovoid capsule up to 18 mm × 7 mm, yellowish brown, dehiscing loculicidally, many-seeded. Seeds c. 3.5 mm long, with very narrow wings.
Other botanical information
Aloe comprises about 450 species in Africa and Arabia, of which c. 315 occur in mainland Africa, c. 100 are endemic to Madagascar or the Indian Ocean islands (including the former Lomatophyllum) and c. 50 occur in Arabia. The taxonomy is complicated by the occurrence of interspecific hybrids both in the wild and in cultivation. Aloe arborescens is a morphologically very variable species.
Growth and development
In southern Africa Aloe arborescens flowers in June–July.
Ecology
Aloe arborescens occurs in montane grassland among rocks, in open evergreen forest and in coastal forests from sea-level to 2100(–2800) m altitude.
Propagation and planting
Aloe arborescens can be propagated by seed and by stem cuttings of 3–10 cm long. It can also be multiplied by tissue culture methods.
Yield
The contents of aloin, aloeresin and aloenin are highest in the leaves that grow high on the branch. Repeated pruning increases the content of these compounds in the dry exudate of the regrown parts from 10% to 85%.
Genetic resources
In Zimbabwe Aloe arborescens has a protected status. As it is widely cultivated for ornamental purposes there are no major threats. All Aloe species, except Aloe vera (L.) Burm.f., are listed by CITES and all international trade of plants and products should be regulated.
Breeding
In the wild, hybrids of Aloe arborescens with a number of other species occur. Hybrids with Aloe ferox Mill. are common and are of interest as garden ornamentals. There are no indications that breeding is actively undertaken, although there is discussion in the literature of Japanese cultivars. Once gel production becomes important, selection for larger leaf size and low anthraquinone content would be indicated.
Prospects
Aloe arborescens is, surprisingly, little used as a medicinal in its native range and surprisingly highly esteemed in Asia and the Mediterranean. The chemistry is subject of intensive study but husbandry aspects have not yet been published in an accessible form. Future developments will depend on competitive advantages of Aloe arborescens over Aloe vera.
Major references
• Coates Palgrave, K., 1983. Trees of southern Africa. 2nd Edition. Struik Publishers, Cape Town, South Africa. 959 pp.
• Kuzuya, B., Shimpo, K. & Beppu, H., 2004. Aloe lectins and their activity. In: Reynolds, T. (Editor). Aloes: the genus Aloe. CRC Press, Boca Raton, Florida, United States. pp. 88–110.
• Newton, L.E., 2001. Aloe In: Eggli, U. (Editor). Illustrated handbook of succulent plants: Monocotyledons. Springer-Verlag, Berlin, Germany. pp. 103–186.
• Yagi, A., 2004. Bioactivity of Aloe arborescens preparations. In: Reynolds, T. (Editor). Aloes: the genus Aloe. CRC Press, Boca Raton, Florida, United States. pp. 333–351.
Other references
• Beppu, H., Kawaib, K., Shimpoa, K., Chiharaa, T., Tamaia, I., Idaa, C., Uedaa, M. & Kuzuyaa, H., 2004. Studies on the components of Aloe arborescens from Japan - monthly variation and differences due to part and position of the leaf. Biochemical Systematics and Ecology 32(9): 783–795.
• Carter, S., 2001. Aloaceae. In: Pope, G.V. (Editor). Flora Zambesiaca. Volume 12, part 3. Royal Botanic Gardens, Kew, Richmond, United Kingdom. pp. 48–98.
• Chauser-Volfson, E. & Gutterman, Y., 2004. Influences of leaf pruning on the content of the secondary phenolic metabolites barbaloin, aloeresin and aloenin, in the leaves of Aloe arborescens. South African Journal of Botany 70(4): 582–586.
• Furukawa, F., Nishikawa, A., Chihara, T., Shimpo, K., Beppu, H., Kuzuya, H., Lee, I.-S. & Hirose, M., 2002. Chemopreventive effects of Aloe arborescens on N-nitrosobis(2-oxopropyl-)amine-induced pancreatic carcinogenesis in hamsters. Cancer Letters 178(2): 117–122.
• Gutterman, Y. & Volfson, C., 2000. Peripheral defence strategy: variation of barbaloin content in the succulent leaf parts of Aloe arborescens Miller (Liliaceae). Botanical Journal of the Linnean Society 132(4): 385–395.
• Kawai, K., Beppu, H., Shimpo, K., Chihara, T., Yamamoto, N., Nagatsu, T., Ueda, H. & Yamada, Y., 1998. In vivo effects of Aloe arborescens Miller var. natalensis Berger (Kidachi aloe) on experimental Tinea pedis in guinea-pig feet. Phytotherapy Research 12: 178–182.
• Kodym, A., Grzesowiak, E., Partyka, D., Markcinkowski, A. & Kaczynska-Dyba, E., 2002. Technology of eye drops containing aloe (Aloe arborescens Mill.-Liliaceae) and eye drops containing both aloe and neomycin sulphate. Acta Polonial Pharmaceutica 59: 181–186.
• van Wyk, B.E. & Gericke, N., 2000. People’s plants: a guide to useful plants of southern Africa. Briza Publications, Pretoria, South Africa. 351 pp.
• Umano, K., Nakahara, K., Shoji, A. & Shibamoto, T., 1999. Aroma chemicals isolated and identified from leaves of Aloe arborescens Mill. var. natalensis Berger. Journal of Agricultural and Food Chemistry 47(9): 3702–3705.
Sources of illustration
• Coates Palgrave, K., 1983. Trees of southern Africa. 2nd Edition. Struik Publishers, Cape Town, South Africa. 959 pp.
Author(s)
C.H. Bosch
PROTA Network Office Europe, Wageningen University, P.O. Box 341, 6700 AH Wageningen, Netherlands


Editors
G.H. Schmelzer
PROTA Network Office Europe, Wageningen University, P.O. Box 341, 6700 AH Wageningen, Netherlands
A. Gurib-Fakim
Faculty of Science, University of Mauritius, Réduit, Mauritius
Associate editors
C.H. Bosch
PROTA Network Office Europe, Wageningen University, P.O. Box 341, 6700 AH Wageningen, Netherlands
M.S.J. Simmonds
Royal Botanic Gardens, Kew, Richmond, Surrey TW9 3AB, United Kingdom
R. Arroo
Leicester School of Pharmacy, Natural Products Research, De Montfort University, The Gateway, Leicester LE1 9BH, United Kingdom
A. de Ruijter
PROTA Network Office Europe, Wageningen University, P.O. Box 341, 6700 AH Wageningen, Netherlands
General editors
R.H.M.J. Lemmens
PROTA Network Office Europe, Wageningen University, P.O. Box 341, 6700 AH Wageningen, Netherlands
L.P.A. Oyen
PROTA Network Office Europe, Wageningen University, P.O. Box 341, 6700 AH Wageningen, Netherlands
Photo editor
A. de Ruijter
PROTA Network Office Europe, Wageningen University, P.O. Box 341, 6700 AH Wageningen, Netherlands

Correct citation of this article:
Bosch, C.H., 2006. Aloe arborescens Mill. In: Schmelzer, G.H. & Gurib-Fakim, A. (Editors). Prota 11(1): Medicinal plants/Plantes médicinales 1. [CD-Rom]. PROTA, Wageningen, Netherlands.
Distribution Map wild


1, plant habit; 2, part of inflorescence.
Redrawn and adapted by Achmad Satiri Nurhaman



plants with inflorescences


inflorescence


inflorescence