A castor bean (Ricinus communis) is a not a true bean, but a derivative of the spurge family (Euphorbiacea) that is manifested by seed-producing deep-rooted perennials. It is actually a tall, leafy plant that originated in tropical South Africa, and is now found in many tropical and temperate climates worldwide.

The plant produces clusters of spiny pods that each contain an average of three poisonous seeds, which are black or brown in color and strongly resemble a tick.

Although all parts of the castor bean are actually poisonous, it is the seeds that are the most highly toxic. The toxins found within the castor bean are ricin, and Ricinus communis agglutinin, or RCA. Ricin is a strong cytotoxin, meaning that it targets the cells of a particular organ, while RCA is a member of the hemagglutinin class, a toxin that is targeted specifically at red blood cells. If any part of the castor bean is ingested, symptoms of abdominal pain, diarrhea, and vomiting will occur within hours. In addition, severe dehydration, decrease in urination, as well as a drop in blood pressure tend to occur over a period of days. Death is often possible in the absence of appropriate medical intervention.

Although toxic if ingested in its pure form, there are many medicinal and practical uses for the castor bean. For instance, the bitter-tasting castor oil has been used for years as an antidote for various digestive problems. This naturally occurring oil is also a common ingredient in such things as paint, varnish, and high-performance motor oils.