Citrullus is a small but economically significant genus in the gourd family (Cucurbitaceae), native to Africa and parts of Asia. Best known for the widely cultivated watermelon (Citrullus lanatus), the genus also includes wild relatives such as the bitter colocynth (Citrullus colocynthis) and the desert-adapted citron melon (Citrullus caffer). Members of Citrullus typically form sprawling vines with lobed leaves and produce fleshy, often sweet or aromatic, melons that have been domesticated and bred for centuries. Beyond the juicy fruit enjoyed fresh or juiced, several wild species provide important genetic traits—such as drought tolerance and disease resistance—that underpin modern breeding programs and help secure food crops in challenging environments.

Citrullus ecirrhosus, commonly known as Namib tsamma, is a species of perennial desert vine in the gourd family, Cucurbitaceae, and a relative of the widely consumed watermelon (Citrullus lanatus). It can be found in both Namibia and the Cape Provinces of South Africa, particularly the Namib Desert. It is the sister species to the bitter melon, Citrullus amarus with which it shares hard, white and bitter flesh.

The vines can crawl for up to two metres, and it has yellow flowers. As a desert plant, it is a hardy species, surviving with little water and strong sunlight. The leaves form annual stems which die back each year. The plant relies on water deep in the ground and morning fogs. It is an important source of water for numerous desert fauna. The bitter-tasting fruit it produces are known as tsamma melons.

The Namib tsamma is found in Succulent Karoo habitat in dry watercourses. It has a limited distribution in South Africa. Its range is from the Richtersveld up to the western Namib in Namibia.

Experiments done by Simmons, Jarret, Cantrell, and Amnon in 2019 introduced the hybridisation of Citrullus ecirrhosus and Citrullus lanatus developed a cultivated watermelon capable of resistance to pests such as whiteflies (Bemisia tabaci). The hybrid developed whitefly resistance while still retaining traits of watermelon (Citrullus lanatus). While the hybrid did not offer total resistance, it was better protected than regular grown watermelons.