Plant story: desert rose (Adenium obesum)

Desert rose was first found and described in Kenya in 1752 by P. Forsskal, a German scientist. It is the only species in the genus Adenium within the Flora of tropical East Africa region. Worldwide, the species is planted as a major ornamental, though it is known to be poisonous.

Adenium obesum at Tharaka. (Photo: P. Kariuki)

Description

Adenium obesum is a succulent shrub or small tree growing up to 0.4-6m high. Trunk sometimes swollen at the base and the bark is usually smooth and grey in colour. Stems exude a milky sap. It produces leaves that are spatulate, dark green, deciduous, fleshy and spirally arranged, clustered at the tips of the shoots. Flowers corolla are showy, pink to red, funnel-shaped with five distinct pinkish or light red lobes. Its fruits are grey to pale grey-brown, sometimes fringed with pink. There are tufts of hairs on the seeds.

Adenium obesum (Forssk.) Roem. & Schult.
Common name: desert rose
Vernacular name: Mucigongo (Tharaka)

Ecology and distribution

The plant grows in dry bush land, especially in rocky sites and also in the woodlands at altitudes between 0 - 1,200m in Kenya, Uganda, Tanzania, Somalia, Saudi Arabia, Yemen and Oman among other countries. The plant successfully grows in low hot arid areas and withstands heat in desert ecosystems. During the dry seasons most of the leaves drop off leaving flowers displaying unique natural beauty.

Conservation

Although the plant is common elsewhere within its natural range, only a few individuals remain in Tharaka. The declining wild population in Tharaka is believed to be as result of the plant being associated with witchcraft and consequently frequent decimation in-situ. Locally, the Tharaka people report that it is the only plant species birds do not nest on, due to high levels of poison. During the Useful Plants ethno-botanical surveys, local guides were surprised when voucher specimens were collected for the EA herbarium, while seeds of the plant have been collected and conserved ex-situ at the National Genebank of Kenya with duplicate collections secured at the Royal Botanic Gardens, Kew. We never know when seeds from this poisonous plant could hold the key to curing deadly disease epidemics recorded in the recent past on earth.

Uses

Whilst the plant is recognised as poisonous, it is also used for witchcraft and medicinal purposes among the Tharaka community. Precisely, the bark of the plant is chewed as an abortifacient while powdered stems are rubbed on livestock skins to control the level of live fleas and lice. However, outside Kenya, a root decoction from the species is used as nose drops for rhinitis in Somalia, while in Saudi Arabia the plant sap and bark are used as remedy for bone dislocation, rheumatism, sprains, paralysis, swellings, wounds and skin infections.

A visit by the ethno botanical team of the Useful Plants Project revealed just how scarce this plant is in the region. Based on the information obtained from the local people and noting that the team just counted five individuals during their survey, it was concluded that this plant is usually eliminated immediately it is sighted, and the therefore the team has targeted this species and is planning to cultivate it on farm and collect the seeds for its ex-situ conservation at the the Genebank of Kenya and at the MSB through the project..

References

1. http://en.wikipedia.org/wiki/Adenium accessed on 24th July 2009
2. Omino, E. A. (2002). Flora of Tropical East Africa, Vol, page 1.
3. Useful Plants Project field survey.
4. Schmelzer, G. H. and Gurib-Fakim, A. (2008). Plant Resources of Tropical Africa 11 (1)