Euphorbia horrida is a wonderful example of convergent evolution in fact it resemble incredibly to some new world cacti.

Family: Euphorbiaceae

Scientific name: Euphorbia horrida Boiss

Common name: African Milk Barrel

Origin: South Africa (lower Great Karoo) Found in the Wittepoort Mts. in the Willowmore District, var. striata is found 24km north of Steyterville, var. noorsveldensis is found 18km to the north of Jansenville, var. major is found 30km north of Willowmore.

Conservation status: Listed in CITES appendix 2.

Euphorbia horrida is a wonderful example of convergent evolution in fact it resemble incredibly  to some new world cacti. 

Description:  Spiny succulent  shrub with irregular basally clumping stems.
Stem: Erect, cylindrical 100 to 150 mm thick, up to 75 (150) cm tall.
Ribs: 10 to 20, wing-like, prominent.
Spines: The formidable rows of spines up to 40 mm long are actually the dried remnants of its flower stalks and are very rigid.
Flower: Very small green and yellow solitary cyathia, pedunculate. Involucre finely hairy with 5 glands and 5 large lobes. Involucres glands are green, blooms in summer.

Note: This plant is somewhat variable with many varieties and forms, and perhaps natural hybrids between it and taller Euphorbias, giving rise to the big, spiny forms like E. horrida noorvalescens, furthermore there are several other similar Euphorbia species (particularly Euphorbia polygona) which often looks a lot like some of the forms.
E. horrida and E. polygona are hard to tell apart only by body characteristics, at least when the plants are young. The only certain characteristic is in their cyathia. E. horrida bears green cyathia that sometimes may turn brownish with the age. The cyathia of E. polygonaare red to deep purple.

Euphorbia horrida  is a wonderful example of convergent evolution.  In fact it incredibly resembles a spiny cactus.

Cultivation: It is a pretty easy species, it grow well in a very draining mineral potting substrate but it isn't picky about soil, the area where this plant is native receives rains in both winter and summer, so it can be watered moderately all year around (except in the coldest month of the winter as it rot easily especially if over wet ) During the summer, they enjoy average feeding and watering. Mature healthy plants are tough and can also be grown out of where frost is not too severe , it can tolerate temperatures down -4°C (-10° C if the roots are kept dry). It like Light shade to full sun, but different clones vary in their tolerance of full sunshine. The general rule is that the smaller and rounder the variety, the less it can tolerate full sunshine.

Propagation: It is propagated from seed sown during spring or summer. Germination occurs within 3 weeks but it can be reproduced by cuttings (The larger forms tend to branch enthusiastically and offsets are readily available) if you remove an offset, remember to let it dry for a week or so, letting the wound heal (cutting planted to soon easily rot before they can grow roots). It is better to wash the cut to remove the latex.
Flowering can be achieved within 5-8 years.

Warning: As with all other Euphorbias when a plant get damaged it exudes a thick white milky sap known as latex. This latex is poisonous and may irritate skin, and pay extreme attention not to get any in your eyes or mouth.
Cultivated plants must be handled carefully.

The species name 'horrida' comes from the Latin for spiny referring to the formidable rows of spines up to 40 mm long. If the spines weren't deterrent enough, they have also a poisonous, corrosive sap.