Castor oil plant can reach a height of 2–3 m in a year (if sown early, under glass, and kept at a temperature of around 20°Celsius/68°Fahreheit until planted out ).
The glossy leaves are 15–45 cm long, long-stalked, alternate and palmate with 5–12 deep lobes with coarsely toothed segments. Their colour varies from dark green, sometimes with a reddish tinge, to dark reddish purple or bronze.
The stems and the spherical, spiny seed pods also vary in pigmentation. The pods are more showy than the flowers (the male flowers are yellowish-green with prominent creamy stamens and are carried in ovoid spikes up to 15 cm long; the female flowers, borne at the tips of the spikes, have prominent red stigmas).
Terminating stems are panicle-like inflorescences of green monoecious flowers, the stalked female flowers above the male flowers below, both without petals.
The fruit is a spiny, greenish capsule with large, oval, shiny, bean-like, highly poisonous seeds with variable brownish motling.
Nomenclature
The name Ricinus is a Latin word for tick; the seed is so named because it has markings and a bump at the end which resemble certain ticks. The common name "castor oil" likely comes from its use as a replacement for castoreum, a perfume base made from the dried perineal glands of the beaver (castor in Latin). It has another common name, Palm of Christ, or Palma Christi, that derives from castor oil's ability to heal wounds and cure ailments.
Habitat and growth
Although castor is indigenous to the southeastern Mediterranean region, Eastern Africa, and India, today it is widespread throughout tropical regions. Castor establishes itself easily as an apparently "native" plant and can often be found on wasteland. It is widely grown as a crop in Ethiopia. It is also used extensively as a decorative plant in parks and other public areas, particularly as a "dot plant" in traditional bedding schemes. Of the red and white variety, the red is seen as an ornamental plant, the white is used medicinally.
Castor oil seed output in 2006
Although monotypic, the castor oil plant can vary greatly in its growth habit and appearance.
It is a fast-growing, suckering perennial shrub which can reach the size of a small tree (around 12 m), but it is not hardy. However it grows well outside, at least in Southern England, and the leaves do not appear to suffer frost damage in sheltered spots, where it remains evergreen. In areas prone to frost it is usually shorter and grown as if it were an annual.
Selections have been made by breeders for use as ornamental plants: 'Gibsonii' has red-tinged leaves with reddish veins and pinkish-green seed pods; 'Carmencita Pink' is similar, with pinkish-red stems; 'Carmencita Bright Red' has red stems, dark purplish leaves and red seed pods; all grow to around 1.5 m tall as annuals.'Impala' is compact (only 1.2 m tall) with reddish foliage and stems, brightest on the young shoots; 'Red Spire' is tall (2–3 m) with red stems and bronze foliage; 'Zanzibarensis' is also tall (2–3 m), with large, mid-green leaves (50 cm long) with white midribs. (Heights refer to plants grown as annuals.)
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