1. Ricinus communis L. (castor oil plant, castor bean)

Map 1685, Pl. 384 h, i

Plants annuals (becoming shrubs or small trees in tropical regions), monoecious, with clear sap, glabrous (lacking stinging and nonstinging hairs). Stems 100–500 cm long, erect or ascending, branched, sometimes somewhat glaucous, usually hollow between the nodes. Leaves alternate, long-petiolate, the petiole with usually several large, saucer-shaped glands positioned mostly at the base and tip, peltate, the petiole attached well away from the blade margin. Leaf blades 10–90 cm long and wide, more or less circular, palmately 6–11-lobed, the lobes triangular to more commonly elliptic or ovate, tapered to a sharply pointed tip, the margins coarsely and sharply toothed, pinnately veined. Stipules fused into a membranous 2-lobed sheath, 12–20 mm long, tan or purplish-tinged, shed early and leaving a circular scar around the stem. Inflorescences terminal but often appearing axillary or lateral and opposite the leaves, racemes or less commonly narrow, racemelike panicles, each with clusters of staminate flowers toward the base and clusters of all pistillate or mixed staminate and pistillate flowers toward the tip, the latter rarely with a few perfect flowers, subtended by a papery lanceolate to ovate bract at the base, the flowers individually sessile or relatively short-stalked. Calyces deeply 3–5-lobed, 2–5 mm long (in pistillate flowers usually shed as the flower opens), ovate, sharply pointed at the tip. Petals absent. Nectar disc absent. Staminate flowers with numerous free stamens, the filaments more or less fused into several clusters toward the base and irregularly several-branched, the anthers sometimes more than 1,000. Pistillate flowers with the ovary 3-locular and 1 ovule per locule, the 3 styles fused toward the base, bright red to pinkish red, each deeply 2-lobed, the lobes with densely papillose stigmatic regions for most of their length. Fruits 10–16 mm long, 12–16 mm in diameter, not or only slightly lobed (circular or slightly and very bluntly 3-angled in cross-section), red to purplish or pinkish red, the surface with dense, long, soft prickles. Seeds usually 3 per fruit, 8–12 mm long, more or less ellipsoid, slightly flattened, with a knoblike caruncle at the end adjacent to the attachment point, the surface appearing smooth, shiny, mottled with dark brown, light brown and white. 2n=20. June–October.

Introduced, uncommon and sporadic (native of Africa, India; introduced nearly worldwide, in the U.S. in the southwestern, southeastern, and northeastern quarters of the country). Railroads, roadsides, and open, disturbed areas.

Castor oil is extracted from the seeds of this species and is used in medicine as a purgative, but it is also important in the manufacture of paints, inks, plastics, soaps, and linoleum (Webster, 1967). Cultivation of R. communis as a crop in the United States has declined, but the species is widely grown as an ornamental, especially in the warmer portions of the country. The seeds are extremely poisonous because of concentrations of the phytotoxin ricin (a complex glycoprotein) in the seed coat. Because the hard seed coat sometimes can pass through the digestive tract intact, accidental ingestion of seeds sometimes does not lead to poisoning. However, if seeds are chewed or crushed, severe poisoning can result if even small numbers are ingested, leading to strong abdominal pain, reduced blood pressure, hypothermia, excessive salivation, diarrhea (sometimes bloody), weakness, trembling, anorexia, sweating, vomiting, sudden collapse, and sometimes seizures, coma, and death (Burrows and Tyrl, 2001). The leaves are also poisonous, but to a lesser degree than the seeds.