structural:expansion
Taxonomy

Cucurbita was formally described in a way that meets the requirements of modern botanical nomenclature by Linnaeus in his Genera Plantarum, the fifth edition of 1754 in conjunction with the 1753 first edition of Species Plantarum. Cucurbita pepo is the type species of the genus. Linnaeus initially included the species C. pepo, C. verrucosa and C. melopepo (both now included in C. pepo), as well as C. citrullus (watermelon, now Citrullus lanatus) and C. lagenaria (now Lagenaria siceraria) (both are not Cucurbita but are in the family Cucurbitaceae.

The Cucurbita digitata, C. foetidissima, C. galeotti, and C. pedatifolia species groups are xerophytes, arid zone perennials with storage roots; the remainder, including the five domesticated species, are all mesophytic annuals or short-life perennials with no storage roots. The five domesticated species are mostly isolated from each other by sterility barriers and have different physiological characteristics. Some cross pollinations can occur: C. pepo with C. argyrosperma and C. moschata; and C. maxima with C. moschata. Cross pollination does occur readily within the family Cucurbitaceae. The buffalo gourd (C. foetidissima) has been used as an intermediary, as it can be crossed with all the common Cucurbita.

Various taxonomic treatments have been proposed for Cucurbita, ranging from 13 to 30 species. In 1990, Cucurbita expert Michael Nee classified them into the following oft-cited 13 species groups (27 species total), listed by group and alphabetically, with geographic origin:

The taxonomy by Nee closely matches the species groupings reported in a pair of studies by a botanical team led by Rhodes and Bemis in 1968 and 1970 based on statistical groupings of several phenotypic traits of 21 species. Seeds for studying additional species members were not available. Sixteen of the 21 species were grouped into five clusters with the remaining five being classified separately: