The Ntumbachushi Euphorbia

The genus Euphorbia is a large and variable group of herbs, shrubs and trees that grow on every continent except Antarctica but have the common feature of milky white latex sap.

Above are some images of common varieties of cultivated, flowering euphorbia, frequently seen around homes in Zambia

There are approximately 75 species of Euphorbia in Zambia from small annual herbs to large succulent trees. Some of the most well-known Euphorbia species in Zambia, and southern Africa for that matter, are the succulent, cactus-like shrubs and trees, with the most recognizable being the Candelabra tree, Euphorbia ingens, growing atop termite mounds in hot dry woodland. 

However, Zambia has nearly a dozen shrubby, succulent Euphorbia species, some of which are narrow endemics and only known from Zambia. Euphorbia williamsonii is one such narrow endemic species known only from rocky quartzite outcrops around Ntumbachushi Falls in Luapula Province.

It grows between 1-2 m tall and wide from a partially exposed tuberous root with a short central stem and numerous upright 3-angled, segmented branches armed with 1 cm long spines. The leaves are tiny and insignificant with the green succulent stems taking over the roll of photosynthesis.

Mature plants produce numerous red and yellow cyathia (specialised Euphorbia inflorescences composed of several small male flowers and a single central female flower) along the upper stem angles which are eventually followed by reddish purple lobed capsules.

Fortunately, despite its small area of occurrence, the population of Euphorbia williamsonii is protected as it is growing in the National Heritage site of Ntumbachushi Falls.

Like all succulent Euphorbia, Euphorbia williamsonii is classified under Appendix II of the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES), meaning that it is illegal to transport or trade plants or plant derivatives across international boundaries.

Still, even with such international protection, we all need to do our part to continue to protect the species and its habitat from degradation.