Characters.—Flowers unisexual. Calyx free (inferior), with various glandular or scaly internal appendages; sometimes wanting. Corolla usually absent, sometimes polypetalous or monopetalous. Stamens definite or indefinite, distinct or monadelphous; anthers 2-celled. Ovary free (superior). Ovules solitary or twin, suspended from the inner angle of the cell. Fruit generally tricoccous, consisting of 3 carpels splitting and separating with elasticity from their common axis, occasionally fleshy and indehiscent. Seeds solitary or twin, suspended often with an aril; embryo enclosed in fleshy albumen; cotyledons flat; radicle superior.—Trees, shrubs, or herbs, often abounding in a milky juice. Leaves opposite or alternate, simple, rarely compound, often with stipules. Flowers axillary or terminal, sometimes inclosed within an involucre resembling a calyx. Some of the Euphorbiaceae are succulent or fleshy, and have a considerable resemblance to Cacteaceae; from which they may in general be distinguished by the presence of an acrid milky juice.
Properties.—Mostly acrids; operating, toxicologically, as acrid, narcotic-acrid, or aero narcotic poisons; and medicinally, as rubefacients, suppurants, emetics, diuretics, and cathartics. The acrid or poisonous principle or principles reside in the roots, stems, leaves and seeds. It is a constituent of the acrid milky juice found in many of the species. "M. Berthollet has recorded a remarkable instance of the harmless quality of the sap in the interior of a plant, whose bark is filled with a milky proper juice of a poisonous nature. He described the natives of Teneriffe as being in the habit of removing the bark from the Euphorbia canariensis, and then sucking the inner portion of the stem in order to quench their thirst, this part containing a considerable quantity of limpid and non-elaborated sap." [Henslow, Botany, In Lardner's Cyclop. p. 217.] In some cases an acrid principle (see vol. i. p. 206) is found in the embryo, but not in the albumen of the seed. Thus Aublet [Histoire des Plantes de la Guiane, t. ii. p. 844.] states that the kernels of Omphalea diandra are edible if the embryo be extracted; but if this be left in, they prove cathartic. In some cases, however, as those of Croton and Ricinus, the albumen also possesses acrid and poisonous properties. The chemical nature of the acrid principle or principles has not been determined. In some cases it appears to be volatile, in others fixed. If it be true that persons have been poisoned by sleeping under the Manchineel tree (Hippomane Mancinella), this species must give out a poisonous vapour. In some cases, however, resin appears to be the active principle; as in the otficinal substance called gum euphorbium.
The expressed oils of the seeds of several of the Euphorbiaceae (as Croton, Ricinus, Jatropha, Euphorbia, and Anda) are purgative; in some cases violently so. They probably owe this to some active principle dissolved in the fixed oil; for the residual oil cake acts as a drastic purgative, in some cases more so than the expressed oil. Soubeiran [Journ. de Pharm,. t. xv. p. 501, 1829.] thinks that some of the eupborbiaceous seeds owe their purgative qualities to resin. The fixed oil of some of the seeds is remarkable for its more ready miscibility with, or solubility in, alcohol, than most other fixed oils.
Some euphorbiaceous plants are devoid of acridity, or possess it in a very slight degree only. Some of these are aromatic, resiniferons, and tonic. Von Buch [Nees and Ebermaier, Méd. Pharm. Bot. Bd i. S. 355] says, the branches of Euphorbia balsamifera contain a mild sweet juice, which is eaten by the inhabitants of the Canary Isles. The aromatic tonic bark of the Croton Eleutheria is another exception to the very general acridity of these plants.
Some of the roots are harmless and nutritious. Others of neighbouring species abound in nutritive starch (e. g., tapioca-starch), which resides in a poisonous juice.