colocynth, (Citrullus colocynthis), hairy-stemmed perennial vine of the gourd family (Cucurbitaceae), native to the Mediterranean region. The colocynth grows in sandy, coastal, or desert soils and commonly spreads vegetatively. The plant has small, pale greenish yellow flowers, forked tendrils, and hairy, deeply cut leaves. The rounded yellow or green fruits have a bitter taste and yield a strong purgative sometimes used in folk medicine.