Castor Oil Plant (Ricinus communis) is an annual or perennial hairless shrub which can grow to 6 m in height. The plant emits an unpleasant aroma when crushed. The stout hollow stems and branches are a dull pale green or red in colour. The large leaves are arranged alternately along the branches and on long, stout, hollow stalks attached off-centre to the bottom of the leaf. The leaf stalks are 10 to 30 cm long. Each leaf blade is 10 to 60 cm across, divided into 7 to 9 pointed triangular segments with toothed edges and conspicuous veins. The leaf blade is glossy and dark reddish-green in colour when young, becoming glossy and green when mature.

Castor Oil Plant produces separate male and female flowers which are on the same plant. The flowers are arranged in erect clusters up to 15 cm long. The flower clusters are at the end of the branchlets (terminal) or in the leaf-stem junction (axillary). Female flowers occur at the top of the spike and male flowers at the bottom. Neither flower has petals. The male flowers have numerous creamy-white stamens and the female flowers have three forked red styles. The fruits are spherical in shape, 1 to 3 cm in diameter, covered in red or green soft spines and contain usually three seeds. The seeds are smooth, grey and silvery-white mottled and 1.2 to 1.5 cm long. They resemble an engorged cattle tick in shape. The seed is scattered over several metres when released explosively from ripe fruits.