The Palma Christi or castor bean plant (Ricinus communis Linnaeus) is a large highly-variable herbaceous (no true wood) member of the Euphorbiaceae considered native to tropical Africa. In temperate areas, the castor bean will grow three to five meters (10 to 15 feet) before succumbing to a killing frost, but in the tropics, it becomes tree-like growing ten to twelve meters (30 to 40 feet). The large palmately lobed leaves are distinctive, as are the softly spined capsules and light to dark brown mottled seeds. Color varies from all green plants to green with red stems and veining to deep burgundy. (See Herbal Folklore, February 2, 2004)

Castor beans are monoecious, staminate (male, stamens) and pistillate (female, pistil) flowers are present on the same plant. Depending upon botanical opinion, the flowers are borne in racemes or panicles; a single spike arises with staminate flowers at the bottom and pistillate flowers at the top. When this spike has developed, it will branch and form additional spikes of flowers. Some authorities consider this habit as a raceme that happens to branch; others consider it a panicle. In the photograph, the staminate flowers appear fuzzy yellow from the load of pollen; the pistillate flowers have already been pollinated and are forming seed capsules.

Having the pollen-bearing flowers below the seed-producing flowers is somewhat unique. On many monoecious plants where the flowers are in the same inflorescence, the staminate flowers are above, so when pollen is shed it falls onto the female flowers. Castor bean gets around this pollination problem; the stamens explosively dehisce (split) flinging most of their pollen in a cloud. Some will pollinate flowers on the same plant; some will carry on the wind to chance upon other castor flowers, but most of the pollen grains are lost on the wind.

The wild type (non-cultivated) varieties do not leave the seeds to fall below the parent plant where they will have to compete for sunlight, nutrients, and water. When ripe, the spiny capsule dries and splits along its three sutures (seams). The sutures usually split rapidly and the explosive force flings the seeds several feet away.

(Compiled from: Hortus Third, Staff of Liberty Hyde Bailey Hortorium, New York State College of Agriculture and Life Sciences, Cornell University, 1976 and "Castor: Return of an Old Crop", R.D. Brigham, New Crops, Wiley, New York, 1993)