'Carissa' is a genus of shrubs or small trees of 2 to 10 m tall, native to tropical and subtropical regions of Africa, Australia and Asia.

They bear smooth, sharp thorns that often are formidable. The leaves are a rich, glossy, waxy green, smooth, simple, entire and elliptic to ovate or nearly lanceolate. They are 2–8 cm long, partly depending on the species, and generally are thick and leathery. In suitable climates some species flower through most of the year. The flowers are nearly sessile, 1–5 cm diameter, with a five-lobed white or pink-tinged corolla.

The fruit of the carissa is an oblong berry which contains numerous small seeds. The green fruit is poisonous, sometimes dangerously so. The ripe fruit are edible, but may be fairly tart, and they taste like a giant cranberry, though some species have fruity flavours with overtones of strawberry or apple. They are rich in Vitamin C, calcium, magnesium and phosphorus. Various birds eat 'Carissa' fruit and distribute the seed.

'Carissa carandas' is grown in several Asiatic countries for its fruit, which is variously used in cooking and in folk medicine.

More Info: en.wikipedia.org