Castor oil (Ricinus communis), also referred to as castor bean, is a type of long-lived perennial shrub from the Euphorbiaceae family. Castor oil is native to Africa, but has been introduced to tropical and subtropical regions worldwide. The plant is known for its distinctive green to reddish purple, spiny fruit capsules that contain large, oval, shiny, bean-like, highly poisonous seeds.

The most toxic part of the plant are it's seeds, which contain ricin-- a highly poisonous lectin (a carbohydrate-binding protein). Seeds ingested at 0.01% of the body weight are lethal to horses; this amount is often contained within a single seed. Clinical signs of poisoning may be delayed 12 hours or more following ingestion of seeds.