cyathium

A cyathium is a specialized inflorescence characteristic of the genus Euphorbia (family Euphorbiaceae). It consists of a cup-like involucre formed by fused bracts, sometimes with petal-like appendages, that encloses a single female flower at the center and a number of reduced male flowers around it. Each male flower is essentially a single stamen; together they may be numerous. The rim or interior of the cup bears one or more nectar glands (cyathophylls) that attract pollinators. The apparent "flower" is therefore a false flower: the true reproductive units are the female gynoecium in the center and the surrounding reduced male flowers. The cyathium is commonly arranged in clusters on the inflorescence stalk, and in many Euphorbia species the surrounding bracts are showy, contributing to a conspicuous display (for example, in poinsettias). Pollination is typically by insects; after fertilization, the single ovary develops into a fruit containing seeds. The cyathium is a diagnostic feature of Euphorbia and helps distinguish the genus from other flowering plants.