What is a Castor Bean Plant?
Castor bean is an evergreen herbaceous or semi-woody large shrub or small tree with a star shaped leaf pattern. The alternate, star-shaped leaves on long petioles can grow over 2½ feet across. Each palmate leaf has 5 to11 deeply incised lobes, with serrated edges and prominent central veins. The species has glossy green leaves, but cultivated selections may have black-purplish, dark red-metallic, bronze-green, or maroon leaves, or bright green leaves with white veins. It also grows wild in Southern California and parts of Florida.
Flowers are produced in dense inflorescences 8-18″ tall at the tops of the stems. The monoecious plants produce male flowers below the terminal female flowers. The flowers do not have petals and are not particularly showy. The ½ inch male flowers each have a cluster of many cream or yellow stamens that shed large amounts of wind-borne pollen. They senesce soon after shedding their pollen. The three conspicuous, star-shaped stigma lobes of the female flowers are bright red with feathery branches.
The little spiny ovary of the female flower develops into a fruit or seed capsule about the size of a golf ball after pollination. The seed pods may be green, pink, or red (depending on the variety), but gradually age to brown. Each spherical, seed capsule is thickly covered with soft flexible spines and has three sections that separate when the seeds are mature. Each section contains one seed that is ejected, often with considerable force, when the carpel splits open.
The ½ inch long seeds, or “beans” (they are not true beans), are produced in large numbers where the growing season is long enough (140 to 180 days). The shiny, intricately mottled seeds are quite attractive, each with their own unique design in colors of black, gray, brown, yellow-brown, maroon and white.
Each seed has a small, spongy caruncle at one end which helps absorb water for germination when planted. Seeds remain viable for 2-3 years. About half the weight of the seed is a thick, yellowish or almost colorless oil that has been used in many industrial applications. The oil was used in ancient times as fuel for lamps, and is now used in paints and varnishes, for water-resistant coatings, in high-performance motor oils, soap, inks, and plastics. Other derivatives are used in polishes, as solid lubricants, in synthetic perfumes and other products. Plants are grown commercially for oil production primarily in India and Brazil, but also in some parts of the U.S. and other countries.