Cucurbita is a taxonomically complex genus of ca. 27 species, all native in the New World. At least five species are cultivated for their edible fruits (incl. gourds, courgettes, vegetable marrows and pumpkins).
Two species are usually claimed as aliens in western Europe, Cucurbita maxima Duchesne ex Lam. and C. pepo but only the latter has been reliably recorded from Belgium. Both species are much alike but all previous records of Cucurbita maxima turned out to be in error. This species (true pumpkin) is apparently much less frequently eaten as a vegetable (Grenfell 1984). Moreover, it is a more southern species (Herklots 1986) and germination is possibly less likely. However, Cucurbita maxima has been confirmed from the British Isles and is therefore tentatively included in the key beneath.
Upper leaf surface usually rough, hirsute hairy (only soft hairy in C. maxima), never with white markings. Sepals linear, with parallel sides === 2
2 Peduncle in fruit deeply furrowed, conspicuously 5-angled, not corky. Leaves deeply 5-lobed, hirsute hairy. Seeds 7-15(-20) mm long === C. pepo
Peduncle terete, becoming corky in fruit. Leaves almost entire or very shallowly lobed, softly hairy. Seeds 20-25(-30) mm long === C. maxima
Bailey L.H. (1929) The domesticated cucurbitas. Gentes Herb. 2(2): 63-115.
Bailey L.H. (1943) Species of Cucurbita. Gentes Herb. 6: 265-322.
Grenfell A.L. (1984) Cucurbitaceae in Britain. BSBI News 38: 13-18. [available online at: http://archive.bsbi.org.uk/BSBINews38.pdf]
Heath P.V. (1994) Commentary on the proposal to conserve Cucurbita Linné. Calyx 4: 53-54.
Herklots G.A.C. (1986) Cucurbita. The Plantsman 8(2): 86-102.
Lira Saade R. (1995) Estudios taxonomicos y ecogeograficos de las Cucurbitaceae latinoamericanas de importancia economica. Systematic and ecogeographic studies on crop genepools 9: XIII + 281p.
Jäger E.J., Ebel F., Hanelt P. & Müller G. (eds.) (2008) Rothmaler Band 5. Exkursionsflora von Deutschland. Krautige Zier- und Nutzpflanzen. Springer Verlag, Berlin: 880 p.
Nesom G. (2011) Towards consistency of taxonomic rank in wild/domesticated Cucurbitaceae. Phytoneuron 2011-13: 1-33. [available online at: http://www.phytoneuron.net/PhytoN-CucurbConsistency.pdf]
Nesom G. (2015) Cucurbita. In: Flora of North America Editorial Committee (eds.), Flora of North America North of Mexico, vol. 6. Oxford University Press, New York: 48-58. [available online at: http://www.efloras.org/florataxon.aspx?flora_id=1&taxon_id=108644]
Singh D. & Dathan A.S.R. (1973) Structure and development of seed coat in Cucurbitaceae: 6. Seeds of Cucurbita. Phytomorphology 22(1): 29-45.
Whitaker T.W. & Bemis W.P. (1975) Origin and evolution of the cultivated Cucurbita. Bull. Torrey Bot. Club 102(6): 362-368.
Whitehouse C.M. (1997) Cucurbita. In: Cullen J. & al. (eds.), The European Garden Flora, vol. 5. Cambridge University Press, Cambridge: 294-295.