Castor oil plant (Ricinus communis). The spiny fruits at the top of the stem contain highly poisonous seeds. They contain ricin, an extremely toxic protein used in biological warfare. The seeds are also used to make castor oil, an effective laxative. The plant is monoecious, having separate male and female flowers on the same plant. The male flowers are below the developing fruits (bottom). They consist of clusters of yellow-cream stamens. All parts of the plant are poisonous.