Prota 11(1): Medicinal plants/Plantes médicinales 1
Bot. Jahrb. Syst. 36: 64 (1905).
2n = 14
Origin and geographic distribution
Aloe divaricata is an endemic of Madagascar and is widespread in the western and southern parts of the island.
A leaf decoction of Aloe divaricata is used as a purgative. A decoction of the leaves or the leaf sap is applied internally and externally to improve healing of bone fractures. The dehydrated exudate, known as ‘Madagascar Aloes’, has been an important article in local and international trade.
Production and international trade
Export of ‘Madagascar Aloes’ by the East India Company dates back to 1630, and prices then were higher than those for ‘Socotrine aloe’, from Aloe perryi Baker. The present production is unclear and there are no export figures.
The internationally traded product ‘Madagascar Aloes’ contains 15–40% anthrone 10-C-glucosides (anthraquinone derivatives) such as aloin, hydroxyaloins and sometimes aloinoside. Aloin and aloinoside are both mixtures of stereoisomers. Aloin is responsible for the laxative properties. On a dry weight basis the exudate of Aloe divaricata contains 18.5% aloin, and the leaf 3%. Aloe divaricata is reported to induce labour by stimulating contractions of the uterine muscles.
Succulent shrub, stem 2–3(–6) m tall, usually sparsely branching from the base or low down, dead leaves persistent over 50–100 cm. Leaves about 30 in a rosette, erect-spreading; stipules absent; petiole absent; blade lanceolate, up to 65 cm × 7 cm, apex obtuse, margin cartilaginous, with deltoid teeth, 5–6 mm long, reddish brown, 15–20 mm apart, blade dull grey-green tinged reddish, exudate drying yellow. Inflorescence heavily branched, consisting of 60–80 terminal, erect racemes, 15–20 cm long, lax, apex acuminate; peduncle up to 1 m long; bracts deltoid, 4 mm long. Flowers bisexual, regular, 3-merous; pedicel 6 mm long; perianth tubular, 2.5–3 cm long, up to 7 mm in diameter, lobes 6, free to base, scarlet or pale pink; stamens 6, exserted; ovary superior, 3-celled, style filiform, stigma head-like, exserted. Fruit an oblong capsule, 25–30 mm × 12 mm long, dehiscing loculicidally, many-seeded. Seeds c. 1.5 cm long, wings 4 mm wide.
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. Based on genome size, most species from Madagascar are considered closely related (with the exception of those formerly placed in Lomatophyllum) although the many different growth forms would suggest otherwise. The species from Madagascar were obviously isolated long ago from the mainland African species.
Apart from Aloe divaricata, a number of other Madagascan Aloe species have recorded medicinal uses. A number of unspecified species are used for sun creams and dandruff lotions. Aloe vaombe Decorse & Poiss. (orthographic variant ‘ vahombe’) is a small tree with an unbranched trunk up to 5 m tall. Skin lesions are treated with leaf juice, and the leaves are boiled in water and drunk to cure yellow fever. Extracts of Aloe vaombe leaves have shown anti-infectious activity when mice were injected with them but no bactericidal activity was detected. In another test with mice, administration of a gel extract called ‘Alva’ reduced the growth rate of fibrosarcoma and melanoma tumours. Aloe macroclada Baker, locally called ‘vahona’, is a solitary plant without stem. The leaves are used to cure ascites, while the leaf pulp is rubbed on the head to treat dandruff. It has a reputation as a traditional anti-carcinogenic. On internet ‘vahona’ gel products are offered for sale with similar properties as for Aloe vera (L.) Burm.f. The leaf sap of Aloe capitata Baker is used as a cathartic and purgative; the whole plant is used to cure dropsy.
Aloe divaricata is mostly found in arid bush vegetation on sandy soils and in coastal thickets, up to 800 m altitude. In dense bush it can grow with a simple stem up to 6 m long.
All Madagascan Aloe species used as medicine are collected from the wild.
Aloe divaricata is considered the Madagascan species with the highest exudate production.
Genetic resources and breeding
All Aloe species except Aloe vera are listed by CITES, and quite a number of Madagascan species appear in Appendix 1. Harvesting from the wild for medicinal and ornamental uses and habitat destruction are major threats to Aloe divaricata.
The Aloe species from Madagascar have not been the subject of systematic ethnobotanical research. It is therefore difficult to determine their potential. Species such as Aloe divaricata, Aloe macroclada and Aloe vaombe could possibly play a role in the worldwide trade of medicinal and cosmetic products and could compete with Aloe vera if they can be cultivated and produced on a large scale.
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Correct citation of this article:
Bosch, C.H., 2006. Aloe divaricata A.Berger. In: Schmelzer, G.H. & Gurib-Fakim, A. (Editors). Prota 11(1): Medicinal plants/Plantes médicinales 1. [CD-Rom]. PROTA, Wageningen, Netherlands.