Euphorbiaceae is the name given to one of the largest families in the plant world, sometimes known as spurges. It includes around 300 genera and 7,500 species, and of these around 870 are regarded as succulent. The IES is mostly concerned with the succulent and semi-succulent members of genus Euphorbia (comprising the former genera Monadenium, Synadenium, Elaeophorbia, Endadenium, and Pedilanthus - now all included into genus Euphorbia) and genus Jatropha.

Many species have a milky latex that exudes copiously when cut, and is more or less caustic. This does not apply to the Jatrophas which have a clear sap. Leaves come in various shapes and sizes, but are often reduced. The stipules, which are generally present, are often reduced to thorns or minute glands. The flowers are always unisexual, male or female, and in some species occur on separate plants. The flowers are often highly reduced in the extreme form with a naked stamen on the male flower and a naked pistil on the female flower. A specialised miniature inflorescence called a cyathium is produced in most Euphorbia species, with a single naked female flower surrounded by several naked male flowers. The whole is enclosed in a cup shaped structure, called the involucre, consisting of a unified calyx from which emerge small, often minutely fringed bracteoles, which act as a protective cover to the involucre. Between these bracteoles are nectar-producing glands. Something resembling a normal flower is produced. In other species, the flowers and inflorescence are more normal in appearance with male and female flowers bearing a five-part calyx and sometimes corolla, with numerous stamens. Female flowers carry a three part pistil over a three part ovary producing three or sometimes more seeds. The fruit is usually an explosive capsule.

The figure of 870 succulent species is not exhaustive, and does not include numerous interesting forms and varieties, as well as undescribed species. There are also countless hybrids of E. milii, some of great horticultural interest, as well as hardy species suitable for the garden or rockery.