Prota 11(1): Medicinal plants/Plantes mιdicinales 1
Syst. veg. 4: 439 (1819).
Orchipeda thouarsii (Roem. & Schult.) Baron (1905).
Wild frangipani (En). Voacanga de Thouars (Fr). Mlindaziwa (Sw).
Origin and geographic distribution
Voacanga thouarsii occurs throughout tropical Africa, from Senegal eastwards through the forest zone to Sudan and Kenya, and south to Mozambique and the east coast of South Africa. It also occurs in Madagascar.
The uses of Voacanga thouarsii are similar to those of Voacanga africana Stapf. The latex or decoctions or infusions of the stem bark, leaves and roots are applied to wounds, boils and sores, and are used to treat gonorrhoea, eczema, fungal infections and scabies. The infusions are also taken to treat heart problems, hypertension and rheumatic afflictions. The latex is put in carious teeth as a temporary filling. In Tanzania the bark, roots and seeds are used as medicine for stomach-ache, snakebites and high blood pressure.
The wood is used in Liberia for hut posts and in Uganda for tool handles and sheaths for knives. The wood is also used as firewood and for making charcoal. The latex was formerly used to adulterate Hevea rubber. It is used as birdlime, e.g. in rice fields in Madagascar and as a glue for fastening handles to knife blades and to repair baskets. The wood is burnt in Sudan and Ghana to produce a salt. The bark yields a fibre, which is used for making hunting nets in East Africa. Voacanga thouarsii is planted along watercourses for soil and water conservation.
In France and Germany tabersonine is extracted from the seed, which is converted into vincamine, a compound widely used in Europe as a depressant of the central nervous system and for the treatment of cerebral vascular disorders in geriatric patients. Seeds are also exported to be used in medicines to treat heart diseases, to lower blood pressure and to treat cancer.
Production and international trade
There is a steady market for Voacanga thouarsii seed, as there is for Voacanga africana. Several hundreds of tonnes of Voacanga seed are exported especially from West Africa, Cameroon and Madagascar to pharmaceutical companies in France and Germany for processing.
In pharmacology indole alkaloids are by far the most important compounds of Voacanga spp., including Voacanga thouarsii. The main alkaloids of the root bark are dimers of the corynanthean-ibogan class dimers, chiefly voacamine, but also voacamidine and voacorine; vobtusine (a dimer of the plumeran-plumeran class) is an important alkaloid from the root bark. In the stem bark, voacamine and congeners predominate, while vobtusine is often also present. Voacangine and voacristine (= voacangarine) are also major constituents. The leaves contain mainly dimeric alkaloids of the corynanthean-ibogan and the plumeran-plumeran classes, but ibogan monomers, including ibogaine and voacangine, are also found. The alkaloid composition of the seeds is similar to other Voacanga species, and consists almost exclusively of the plumeran-class tabersonine (1.61.8%). Voacamine, vobtusine and voacangine have hypotensive, cardiotonic and sympatholytic activities. The leaves of specimens from Madagascar were shown to contain the flavonoid-glycosides rutin and kaempferol-3-glucoside. Callus grown in vitro from leaf material containing 0.9% alkaloids produced 0.3% alkaloids (0.2% in the tissue and 0.1% excreted into the medium). Tabersonine was the only alkaloid isolated from the culture; it was not a constituent of the leaves.
The wood is reddish brown, tough and difficult to saw. It does not plane smoothly because of picking up of grain.
Small tree up to 15(20) m tall, repeatedly dichotomously branched, glabrous to shortly hairy on all parts; trunk up to 40(80) cm in diameter; bark pale grey-brown, smooth, with some white latex. Leaves opposite, simple and entire; ocrea widened into stipules in the axils of petioles; petiole 825 mm long; blade narrowly obovate, 625 cm Χ 29 cm, base cuneate or decurrent into the petiole, apex acuminate, leathery, pinnately veined with 1220 pairs of lateral veins. Inflorescence a cyme, 2 together in the forks of branches, few-flowered; peduncle 514 cm long, stout; bracts ovate, up to 10 mm Χ 7 mm, apex rounded, deciduous. Flowers bisexual, regular, 5-merous, sweet-scented; pedicel 815 mm long; calyx campanulate, 1016 mm long, fleshy, lobes broadly ovate, apex rounded, with hyaline margin, erect, clasping the corolla tube and shed together with the corolla; corolla tube almost cylindrical, 1723 mm long, twisted, lobes broadly obcordate, 1930 mm Χ 2843 mm, spreading or recurved, pale green, creamy or white; stamens inserted 34 mm below the corolla mouth, exserted for 23 mm, anthers sessile, narrowly triangular, base sagittate, apex acuminate; ovary superior, consisting of 2 separate carpels, surrounded by a ring-shaped disk, style gradually thickened at apex, pistil head 11.5 mm long with a fimbriate ring at base. Fruit consisting of 2 separate globose follicles 410 cm in diameter, pale and dark green spotted, 2-valved, many-seeded. Seeds obliquely ovoid or ellipsoid, 810 mm long, minutely warty, with shallow grooves, dark brown, aril orange, pulpy. Seedling with epigeal germination.
Voacanga is an Old World genus comprising 12 species, 7 in Africa and 5 in Asia. It is closely related to Tabernaemontana. Voacanga thouarsii plants develop according to the architectural growth model of Leeuwenberg determined by a monopodial orthotropic trunk, which ends in a terminal inflorescence. After flowering the 2 uppermost axillary buds develop into branches, so that the growth is sympodial; the infructescence seems to be axillary. Voacanga thouarsii flowers throughout the year.
Voacanga thouarsii occurs mostly in semi-deciduous forest and savannas, often in moist localities, from sea-level up to 600 m altitude. It easily colonizes disturbed habitats.
The fruits of Voacanga thouarsii are collected immediately when they open, and the seeds are removed from the arils. Seeds can be sown directly; soaking overnight in cold water may hasten germination. Since the seeds are sticky, they should be stored in a medium such as sand. Voacanga thouarsii regrows well when coppiced or pollarded.
Genetic resources and breeding
In West Africa destructive harvesting of the fruits of Voacanga thouarsii for the international pharmaceutical market is a cause for concern. The extensive collection of fruits to obtain the seeds limits regeneration. On the other hand, the adaptation of Voacanga thouarsii to disturbed habitats, its wide distribution and its quick regeneration ability lower the risk of genetic erosion.
Many of the indole alkaloids found in Voacanga thouarsii and related species display very distinct and interesting pharmacological activities. Some of them have potential as candidates for lead compounds in the development of future medicines.
In some regions the extensive harvesting of fruits and the cutting of trees to gather fruits to fulfil the demand for seeds of large pharmaceutical companies are causing rapid disappearance of Voacanga thouarsii from the wild. Domestication and the development of adapted agronomic practices are needed to counteract this development. In the meantime, local authorities should be vigilant in stopping the destructive harvesting to preserve the species for the future.
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Correct citation of this article:
Schmelzer, G.H., 2006. Voacanga thouarsii Roem. & Schult. In: Schmelzer, G.H. & Gurib-Fakim, A. (Editors). Prota 11(1): Medicinal plants/Plantes mιdicinales 1. [CD-Rom]. PROTA, Wageningen, Netherlands.
leafy twig and opened fruit