Crown-of-thorns (Euphorbia milii var. splendens) is a slow-growing plant with a rambling growth habit. Individual plants can grow to 5 feet by 3 feet on this Madagascar native that may be extinct in the wild. Its 5- to 6-sided fleshy, thorny stems are adorned with short, oblong leaves that are slightly larger than the species. The flowers—yellow cyathia enclosed by red bracts—require full sun, moderate temperatures, and low humidity. It's a perfect addition to the desert garden.

The name of this plant is from the Latin euphorbea for Euphorbus, a Greek physician in 1 C.E. who used the sap medicinally. The milky latex sap of this Madagascar native "bleeds" when stems are cut; the bleeding can be stopped by immersing the stems in warm water. The Euphorbiaceae are a very large family, containing more than 2,000 species, including the popular poinsettia.