Castor plant

Article By:

Zimmerman, Leroy H. U.S. Department of Agriculture, Tucson, Arizona.

Last reviewed:January 2021

DOI:https://doi.org/10.1036/1097-8542.112700

A coarse, erect, annual herb plant, Ricinus communis, belonging to the spurge family (Euphorbiaceae). The castor plant (Ricinus communis) is a member of the spurge family (Euphorbiaceae) in the order Malpighiales. The plant varies greatly in height and in the color of its foliage and stems. There is also great variety in the color, size, and oil content of the plant's seeds, which are called castor beans (see illustration). The palmately lobed leaves of the castor plant are borne more or less alternately. The main stem is terminated by a raceme (the primary raceme; note that a raceme is an inflorescence on which flowers are borne on stalks of equal length on an unbranched main stalk that continues to grow during flowering). After appearance of the primary raceme, branches on the main stem are each in turn terminated by a raceme. Growth continues sequentially as long as the plant lives, with branches arising from recently terminated branches. Thus, a plant can have racemes in all stages of development. Mature racemes mostly have 10 to 70 capsules, with each capsule containing three seeds. In frost-free areas, the castor plant can attain a height of 9–11 m (30–36 ft). Castor seeds are poisonous and also contain allergens. See also: Allergy; Malpighiales; Poison; Poisonous plants; Seed

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