Although the common name is Apple of Sodom, Calotropis is a poisonous plant. Other common names include Rubber bush and King's crown, and sometimes it is known by the synonym Asclepias procera.
The genus Calotropis is part of the Apocynaceae family and it is native to North Africa, Tropical Africa, Asia and Indochina. Caloptropis forms a spreading shrub or medium tree 2.5 to six metres high. It has a tap root that can go down four metres and a fibrous root system. Its ability to find water deep in the soil helps it to live during periods of drought and its ability to send up suckers from its fibrous mat of roots makes it a useful plant to prevent soil erosion. However its strong survival instincts have made it unwelcome in some temperate countries where it can grow unchecked and soon swamp other plant species.
The fruits are apple-like, green and about 10cm in diameter. When crushed or hit they make an audible popping sound as they are filled mainly with air. In the centre is a small seed pod filled with fine silk. This silk was once collected to fill pillows or strands of it were twisted together to make wicks for lamps.
The white milky latex that exudes from the cut stems of Calotropis is poisonous and was once used as a poison for arrowheads. The mature stems are covered with a thick cork-like bark and the grey-green leaves are 15-30cm long and waxy. Fibres from the stems were used to make rope, nets and paper. The flowers are quite unusual, they are small white or greenish white at the base and purplish at the pointed tips. In the centre of each flower is a raised 'crown'. The plant is a food source for the Monarch caterpillar and attracts lots of pollinating insects.
Calotropis was first described by a Roman Jewish historian called Josephus who found it growing near Sodom. It is mentioned in both the Mishnah and the Talmud (its fibres cannot be used as wicks during the Sabbath).