Euphorbia horrida ｜Euphorbia polygona

Origin

Both species are endemic to South Africa.

• Euphorbia horrida: Primarily found in the Eastern Cape and parts of the Western Cape (specifically the Little Karoo and Great Karoo regions).

• Euphorbia polygona: Primarily restricted to the Eastern Cape Province, often found in the Uitenhage and Albany districts. Both were documented in the late 18th to early 19th centuries and have since become iconic symbols of African succulent flora.

Habitat

They share similar ecological niches, thriving in arid, rocky slopes and karroid scrublands.

• They are typically found nestled among sandstone or quartzite rocks, which provide both mineral-rich drainage and some protection for young plants.

• The habitat is characterized by low, erratic rainfall and extreme temperature fluctuations. To survive, these plants have evolved a columnar, rib-heavy structure that allows for expansion during rains and provides self-shading to reduce heat stress.

Description

While both are dioecious (separate male and female plants) and look like cacti (convergent evolution), they have distinct ornamental features:

Euphorbia horrida

• Growth Habit: Initially globose, becoming a stout, clumping cylinder with age. It can reach up to 1 meter in height.

• Ribs & Spines: Known for its deeply sunken valleys between 10–20 sharp ridges. The "spines" are actually dried peduncles (flower stalks) that persist on the plant, giving it a fierce, "horrid" (as per its name) appearance.

• Color: Often exhibits a beautiful glaucous (waxy) blue-gray to silver-white epidermis, which is highly prized by collectors.