Euphorbia is one of the largest and most morphologically diverse genera of flowering plants, encompassing roughly 2,000 species in the family Euphorbiaceae. Its members range from tiny annual weeds to towering trees — Euphorbia ampliphylla of East Africa can reach 30 meters — and from leafy temperate herbs to globe-shaped, ribbed succulents that bear a striking resemblance to cacti. This last resemblance is the source of frequent misidentification: euphorbias and cacti have independently evolved similar forms through convergent evolution, but euphorbias are readily distinguished by their milky white latex, a caustic sap present in every species of the genus.
The defining feature that unites all euphorbias is a specialized inflorescence called the cyathium. What appears at first glance to be a single flower is in fact a tightly clustered structure of highly reduced individual flowers — male flowers reduced to a single stamen, female flowers to a single pistil — enclosed by cup-shaped bracts that often bear glands and may be elaborately colored. This pseudanthium mimics a conventional flower to attract pollinators, making it one of the most sophisticated floral deceptions in the plant kingdom.
The milky latex produced by all species contains diterpenes and triterpenes and is a serious irritant: contact with skin causes burning, contact with mucous membranes can cause extreme pain, and eye contact can result in permanent blindness. Despite this, euphorbias have a long history of human use. Compounds derived from Euphorbia peplus (petty spurge) are the basis for ingenol mebutate, a clinically approved treatment for actinic keratosis. Numerous species serve as live hedging and windbreaks across sub-Saharan Africa. Others have been cultivated as ornamentals for centuries — Euphorbia pulcherrima (poinsettia) is one of the world's most commercially important potted plants.
The genus is broadly divided into four subgenera — Esula, Athymalus, Chamaesyce, and Euphorbia — with molecular work revealing that several formerly independent genera (including Chamaesyce, Monadenium, and Pedilanthus) nest within Euphorbia. The genus is also remarkable for exhibiting all three major photosynthetic pathways: C3, C4, and CAM, reflecting adaptations across an enormous range of climates. Hardy garden euphorbias make imposing domes of lime-yellow cyathia in spring; succulent species from southern African deserts form geometric globes and columns; and dozens of species support specialist insect communities, including spurge hawkmoths whose larvae feed exclusively on Euphorbia foliage.
