watermelon Citrullus lanatus, a fruit quite distinct from the ordinary sweet melons and with a longer history of cultivation. It is a native of Africa, where there were originally two species: the watermelon itself and the very bitter colocynth, which is inedible without being processed but has some food uses as well as some in traditional medicine.
Watermelons were eaten and cultivated in Egypt well before 2000 bc. Surviving wall-paintings clearly show the large green fruits. These are highly refreshing, and especially useful as a source of potable liquid where water supplies are polluted. This advantage encouraged its spread to lands around the Mediterranean and as far east as India and, eventually (10th to 12th centuries ad), China.