Castor oil plant

Castor oil plant (Ricinus communis) is a shrub or small tree of the spurge family (Euphorbiaceae), 1–3 m tall (occasionally to 10 m in the humid tropics), with hollow jointed stems, green or reddish when young, exuding milky sap. The leaves are very large, alternate and peltate, palmately divided into 5–11 toothed lobes, 15–60 cm across, on long glandular stalks; the veins radiate from a point within the blade. The flowers are small, unisexual and monoecious, without petals, borne in spikes: male flowers (yellow stamens) below, female flowers (red stigmas) above; pollination is by wind. The fruit is a soft-spiny capsule splitting into three parts, each holding one seed. The seed is oval with a glossy, mottled grey-brown-black coat and is rich in oil (40–60%) — but contains the extremely toxic protein ricin.

The plant originated in Africa and the Middle East and has been cultivated for its oil for over 4,000 years; it now grows wild and is cultivated throughout the tropics and subtropics. The oil pressed from the seeds (castor oil) is rich in the triglyceride ricinolein, highly viscous and heat-resistant, and is a feedstock for lubricants, hydraulic fluid, plastics, synthetic fibres, paints, cosmetics and even fuel; in medicine it is a stimulant laxative and a folk labour-inducer. Castor seeds are highly poisonous owing to ricin — only a few seeds can kill a child — and must never be eaten; ricin is also a controlled biotoxin. In Vietnam, castor grows wild along roadsides, hedges and waste ground across the lowlands and midlands; the red-leaved form (thầu dầu tía) is grown as an ornamental. Folk medicine applies the leaves to boils and the root or seeds for aches, and the oil for scabies — but with the greatest caution because of its toxicity.