Cucurbita maxima Duchesne ex Lam. (S Am.) - An exceptional and ephemeral alien, probably always from food refuse or sewage sludge. Claimed on many occasions in the past but not reliably recorded before 2017 when it was seen in Kieldrecht (Waasland port area).
This species is much reminiscent of Cucurbita pepo but easily distinguished in the fruiting stage: the fruiting peduncle becomes corky and terete in C. maxima while it is angled and furrowed in C. pepo.
This species (true pumpkin) is apparently much less frequently eaten as a vegetable than C. pepo (Grenfell 1984). Moreover, it is a more southern species (Herklots 1986) and germination is possibly less likely.
Selected literature
Grenfell A.L. (1984) Cucurbitaceae in Britain. BSBI News 38: 13-18. [available online at: http://archive.bsbi.org.uk/BSBINews38.pdf]
Herklots G.A.C. (1986) Cucurbita. The Plantsman 8(2): 86-102.