Euphorbia Obesa Description
Euphorbia obesa can grow to 20 cm in height with a diameter of 9 cm. It is a single-stemmed, unbranched, firm-bodied plant. The stem is usually 8-angled and grooved, subglobose (almost spherical) in shape, elongating and becoming cylindric as it gets older. Younger plants have a rounded sea urchin-like shape. The rotund stem is mottled grey-green in colour with dull purple transverse bands. It has a tapering tap root. The leaves are very rudimentary and soon drop off.
Euphorbia obesa is dioecious, i.e. male and female flowers occur on different plants. All euphorbias have a complex floral arrangement that is termed a cyathium (a cup) and this is the unit of the inflorescence. A cyathium contains many highly reduced male flowers or a single female flower. In Euphorbia obesa, the cyathia appear in summer, from “circular flowering eyes”, situated along the tops of the angles, near the growing tip, on the stem. They are produced on fork-branched peduncles (flower stalks), have minute bracts and are finely hairy. The cyathia are cup-shaped to 3 mm in diameter, expanding in the female. The fruit is a slightly 3-angled capsule , up to 7 mm in diameter that explosively releases small rounded 2mm diameter mottled grey seeds when mature. The peduncles do not persist, and fall off after the seed has been dispersed.
Euphorbia obesa is a rare endemic of the Great Karoo, south of Graaff-Reinet in the Eastern Cape. Over-collecting by collectors and plant exporters almost resulted in the plant becoming extinct in the wild. Today it is protected by national (Nature Conservation) and international (CITES) legislation.
Although Euphorbia obesa is still rare in its habitat it is well established in cultivation. Hundreds of thousands of plants are produced annually by the horticultural trade in America and Europe. This is an example of ex situ conservation and one can safely assume that more plants exist in cultivation than in the plant’s native habitat.
Distribution and habitat
The plants occur in karoo vegetation among Beaufort shale fragments, where they grow in full sun or in the partial shade provided by dwarf karoo shrubs. They are very well camouflaged and difficult to see. The habitat is very stony and hilly with summer rainfall ranging from 200-300 mm per annum, falling mainly in thunder showers. Summers are very hot: the average daily maximum about 26 degrees centigrade and the minimum about 11 degrees centigrade. Light frost occurs during the winter months.