The Euphorbiaceae make up a large and cosmopolitan Family of plants of which the succulent element is but one of many facies. There are estimated to be 300 genera and over 5,000 species, of which one genus. Euphorbia, accounts for two fifths of the species. In the European flora the Family is known only by a handful of small annual or perennial weeds (Euphorbia, the spurges, and Mer-curalis. the dog's mercury, for example). However, most are tropical woody shrubs and trees, including the economically important rubber-bearing genera Hevea and Manihot and the castor oil plant, Ricinus. A common feature of almost all species is a sticky white sap (latex) that exudes from any cut surface. It is generally poisonous and no doubt contributes to the protection of the plants from
chewing and biting creatures: very few will touch Euphorbiaceae. The flowers (20.4) are always unisexual, small and simple in structure. The fruit is typically a three-lobed capsule that at maturity flies apart into three segments, each releasing one seed.
Turning now to the manifestations of succulence, Jatropha, least specialized florally, is discussed in its rightful place in the next chapter, being caudex-forming. This leaves us with five genera of the Tribe Euphorbieae, the most highly evolved in the Family.
one three-lobed ovary topped by a three-lobed style and set on a short stalk (pedicel). Surrounding it are what look like stamens of various ages: each is actually a single male flower reduced to the barest essentials—one stamen with two pollen-bearing anther lobes at the tip. This male flower stands on a tall pedicel with a constriction at the point where it detaches after shedding the pollen. The male flowers are interspersed with hairs and surrounded by a cup-like protective envelope, called an involucre, which bears fringes and nectar glands at the top. A "false flower" having this make-up is known as a cyathium (20.5). Even Linnaeus was deceived into treating it as a single flower, but by starting with the genus Jatropha with separate male and female flowers we can trace an evolutionary series showing progressive reduction of the flowers and their assembly
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