Euphorbia esula

Leafy Spurge

Cyme of Cyathia, Stage II

Regina
13-July-2008

The female flower has reflexed, and male flowers have emerged from the involucre of the central cyathium.

The basic floral unit is a structure known as a cyathium.  The cyathium is composed of a cup-like involucre plus several male flowers, and a single central female flower, that are enclosed by the involucre.  The top margin of the involucre is lobed and contains four, brown, crescent-shaped glands.  The horns on the glands are prominent to absent.  The female flower emerges first from the top of the involucre, followed by the male flowers.  Each cyathium is subtended by a pair of bracts known as cyathophylls.

The cyathia are arranged in dichasial cymes.  The peduncle terminates in a central cyathium, subtended by what I refer to as tier 1 cyathophylls.  Adjacent to the central cyathium are two lateral cyathia, each subtended by what I refer to as tier 2 cyathophylls.  The central cyathium matures first and then withers.  Meanwhile, the lateral cyathia are exserted on lengthening peduncle branches.  Given enough time, each lateral cyathia produces two adjacent cyathia in a similar manner as the original central one, and the structure repeats and multiplies itself.

Most of the cyathia occur within a pseudumbel that terminates the main stem.  The pseudumbel consists of a terminal, sessile cyathium that is subtended by a whorl of pedunculate cymes.  Each of the peduncles is subtended by an involucre leaf.  The involucre leaves form a whorl at the base of the pseudumbel.

The rest of the cyathia occur within cymes terminating peduncles arising as branches from the main stem.  These peduncles can also be somewhat whorled.

The flowers themselves are much reduced.  The male flower consists of a single stamen with a joint at the junction of the pedicel and filament.  The pedicellate female flower consists of a single ovary topped by three bifid styles.  Petals and sepals are absent from both types of flowers.