castor bean, bean produced by Ricinus communis, a plant of the spurge family, widely cultivated as an ornamental. Moles die when they eat the roots. It has long been used as an ordeal poison in parts of Africa. Ricin, the toxic protein found in the bean seeds, can be extracted and used as a poison or chemical weapon, but it is not as poisonous or as readily absorbed as other such weapons. Castor oil is also extracted from the beans.

Large plant (Ricinus communis) of the spurge family, probably native to Africa and naturalized throughout the tropics. It is grown commercially for the pharmaceutical and industrial uses of its oil and for use in landscape gardening because of its handsome, giant, fanlike leaves. The bristly, spined, bronze-to-red clusters of fruits are attractive but are often removed before they mature because of the poison concentrated in their mottled, beanlike seeds. There are hundreds of natural forms and many horticultural varieties of this species.

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