Lindsay is responsible for today's entry. Lindsay writes:

Thanks to Lotus Johnson aka ngawangchodron@Flickr for submitting today's photo (original image | Botany Photo of the Day Flickr Pool).

Prominently featured in this photograph are the cyathia (single: cyathium) of woodspurge. The cyathium is a kind of "false flower" consisting of a cup-shaped involucre bearing several minute stamens (male flowers) and a pistillate flower consisting of an ovary on a long stalk (pedicel). These features are characteristic of every inflorescence in the genus Euphorbia (and its closest relatives), and are found nowhere else in the plant kingdom.

Researchers at the Royal Botanic Gardens, Kew have studied the origins of the cyathium and concluded that it evolved from a more open grouping of flowers called a thyrse. In the thyrse of Euphorbia's ancestors, the terminal female flower was surrounded by cymes of male flowers. With this kind of precursor, researchers presume that the cyathia were eventually formed by a strong condensation of the inflorescence. One of the conclusions derived from this study was that the cyathium is neither a flower nor an inflorescence, but rather a "hybrid" in which regulatory genes that normally control features of individual flowers have overlapped into control of the inflorescence.