Thanks to Jackie Chambers, UBC Botanical Garden horticulturist, for today’s photograph and write-up! Jackie writes:
Medusa’s head euphorbia is a low-growing, sprawling shrub that can reach up to 1m in diameter. It has thick, short, club-shaped branches which can range from 1-3 cm in diameter. There are no spines on this particular Euphorbia, however the stems have a bumpy texture; these are the remains of peduncles, or flower stalks from previous years. The stems are green and photosynthetic. Towards the top of the branches, the plant also produces some smaller, narrower leaves that are deciduous.
The branches arise from a caudex, or swollen stem, which has a primary function water storage. The caudex may be at ground level and visible, but may also be partly buried underground. Caudiciform is the term applied to plants that have caudices.
The inflorescence of the genus Euphorbia is unique in structure and has its own name: cyathium (pl.: cyathia). What appears to be one single flower is in fact a group of flowers, but condensed to simulate one flower. The staminate, or pollen-producing, flowers are tiny and just visible protruding from the lobes of the cyathia in the photos above, while the pistillate flowers extend above and beyond the lobes and staminate flowers. The Plant Heritage site has diagrams and more information on cyathia.
In Euphorbia caput-medusae, the cyathia are held at the tips of the branches, on short peduncles or stalks that are 1 cm long. The cyathia are cup-shaped (1-3cm wide) with 5 glands which are divided at the tips — producing the rather decorative whitish fringed edges. Glands secrete nectar that attracts pollinators. Medusa’s head has a long flowering season in South Africa and can bloom from May to September.
This species is found in sandy, stony slopes in Namaqualand and the southwestern Cape of South Africa. This particular specimen was photographed just outside of Clanwilliam, a small town about 250km north of Cape Town. The town is at the base of the Cederberg Mountains, which are home to many interesting plants.