– Euphorbia coerulescens (2018)

By Chris Walker (July 2018)

My new Plant of the Month “win” is Euphorbia coerulescens, and what a gnarly, fierce beauty it is. Euphorbias are a large genus of plants of over 2,000 different species. They are commonly called spurges, which refers to the purgative nature of the latex substance that serves in the vascular system just under the surface of the plants.

A Greek physician named Euphorbos, who served King Juba of Numidia around 50 B.C. to 23 A.D., used the latex of a particular species of plant for its purgative nature and prescribed its use for the king. King Juba then named the plant after his physician. Much later in 1753, Carl Linnaeus assigned the name to the entire genus. The species name of the plant I won, coerulescens, refers to the bluish color of the stems.

Eurphorbia coerulescens occurs in the Noorsveld desert area of Cape Province, South Africa. It grows alongside other succulent species like Portulacaria afra and is foraged by elephants. E. coerulescens covers large tracts of land in this area, where farmers use it to feed their sheep when drought conditions persist. They cut the stems and let them dry for a while. Once the latex dries out, the caustic affect is greatly reduced.

The plant naturally grows into rather sculptural, upright columns with uneven growth. Generally, the species reaches about 2 to 6 feet tall. E. coerulescens is considered leafless, although some plants develop small, temporary leaflets at the apical tips. In fact, my plant has these leaves, which is an exciting sign of life this spring.

E. coerulescens develops four to six vertical ribs. Thick thorns that grow in pairs form on the edges of the ribs. Small, yellow flowers appear between the thorn pairs. As the flowers fall off, they leave behind scalring along the edges, contributing to the gnarly look of the plant.

Euphorbia flowers exhibit a complex form called a cyathium, in which tiny, minimally formed male flowers surround a single female flower. There are no flower petals, no sepals. The “cupcake” part holding the flowers together is called an involucre. Euphorbias are the only plants known to have this kind of flower head. E. coerulescens flowers in early to mid-spring to early summer.

This plant is rated Zone 9b (annual minmum temperature of 25 degrees F) and prefers a neutral pH of 6.6 to 7.5. It prefers full sun but can tolerate partial shade. E. coerulescens should be grown in a well-draining potting mix. Water well in the active growing season and keep it dry in winter.