Citrullus lanatus is a different genus from cucumber (Cucumis sativus) and melon (Cucumis melo). Bitter colocynth (Citrullus colocynthis) is a separate species.
How it was found
Kew maps Citrullus lanatus as eastern Sahara. Native list: Egypt, Ethiopia, Libya, Sudan-South Sudan. Introduced very widely, including California. Kew’s Species Profile on the same taxon: thought to be native to Africa; some propose the Kalahari region (Botswana, Namibia and South Africa), others northeastern Africa. USDA GRIN native rows emphasize Egypt (south), Sudan, and Kenya (north); GRIN Other: probable origin western or northeastern Africa.
Kew Species Profile: it is thought that watermelon was first domesticated in central and southern Africa; origins are unknown after long cultivation. Same profile: it may have been selected from Citrullus colocynthis, while C. ecirrhosus is thought more likely to be the progenitor based on plastid DNA. UC Kearney/UCCE Fresno: watermelons are considered to have originated in Africa.
How people used it
Kew lists food (also animal food, fuel, environmental and social uses). Kew Species Profile: widely cultivated for edible fruits and as a water source in arid regions of Africa; flesh consumed fresh; seeds eaten in some African and Asian cuisines. UC Kearney trial treats Citrullus lanatus as a fruit crop (seeded, seedless triploid, icebox, and mini types).
Kew lists medicine and poison uses, and its Species Profile lists several traditional uses.
Timeline
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More than 5,000 years ago
Egyptian tombs, African domestication
Kew Species Profile: watermelon seeds and leaves have been found in ancient Egyptian tombs, suggesting it was cultivated there more than 5,000 years ago; first domestication is thought to have been in central and southern Africa.
Kew POWO Species Profile — Citrullus lanatus
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16th century
Across the Atlantic
Kew Species Profile: watermelon is native to Africa and did not reach the Americas until the 16th century. An Old World cucurbit, arriving after contact.
Kew POWO Species Profile
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1629
Seeded watermelons in the U.S. market
UC Kearney/UCCE Fresno organic watermelon trial: older diploid (seeded) watermelons have been a major part of the U.S. market for many years (since 1629).
UCCE Fresno / UC Kearney — Organic Personal Watermelon Variety Trial (2006)
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1916
The accepted name
Kew accepts Citrullus lanatus (Thunb.) Matsum. & Nakai, first published in Index Seminum (TI, Tokyo) 1915–1916: 30 (1916). Homotypic synonym Momordica lanata Thunb. (1794), nom. cons.
Kew POWO
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1939
Seedless triploids in Japan
UC Kearney/UCCE Fresno: seedless (triploid) watermelons were first produced in Japan in 1939 — a diploid × tetraploid cross (2n=22 × 4n=44) yielding a sterile triploid. Large seedless types became popular in U.S. markets later (since 1988 on that PDF).
UCCE Fresno / UC Kearney (2006)
Cool to know
Kew Species Profile: watermelon is Cucurbitaceae with cucumbers (Cucumis sativus), melons (Cucumis melo), loofahs, and pumpkins/squashes (Cucurbita) as relatives — different genera. Epithet lanatus means woolly (hairs on young stems). The generic name Citrullus is a diminutive of Citrus, perhaps referring to spherical fruit.
Kew POWO Species Profile
UC Kearney/UCCE Fresno: older diploid seeded (since 1629), large seedless triploids popular since 1988, icebox 6–12 lb, and seedless mini/personal melons widely available from 2003. Scientific name on that PDF: Citrullus lanatus.
UCCE Fresno / UC Kearney
Kew Species Profile: wild unselected forms tend to bear bitter fruit because of cucurbitacin; cultivated flesh is usually red or yellow, sometimes orange, pink or white; wild fruits much smaller than cultivated ones.
Kew POWO Species Profile
Growing notes for this plant live on the Plant Wiki.
Want watermelon in a San Diego bed? See the seed-starting How-To for planting in this climate. Get a quote or write yourgardenofgold@gmail.com.