
Watermelon ( Citrullus lanatus ( Thunb. ), family Cucurbitaceae ) is a vine-like (scrambler and trailer) flowering plant originally from southern Africa . Its fruit, which is also called watermelon , is a special kind referred to by botanists as a pepo , a berry which has a thick rind ( exocarp ) and fleshy center (mesocarp and endocarp). Pepos are derived from an inferior ovary, and are characteristic of the Cucurbitaceae. The watermelon fruit, loosely considered a type of melon – although not in the genus Cucumis – has a smooth exterior rind (usually green with dark green stripes or yellow spots) and a juicy, sweet interior flesh (usually deep red to pink, but sometimes orange, yellow, or white).
Watermelon is thought to have originated in southern Africa, where it is found growing wild. It reaches maximum genetic diversity there, with sweet, bland and bitter forms. In the 19th century, Alphonse de Candolle claimed the watermelon was indigenous to tropical Africa. Though Citrullus colocynthis is often considered to be a wild ancestor of watermelon and is now found native in north and west Africa, it has been suggested on the basis of chloroplast DNA investigations that the cultivated and wild watermelon diverged independently from a common ancestor, possibly C. ecirrhosus from Namibia.
Evidence of its cultivation in the Nile Valley was found from the second millennium BC.