Cucumis L.
Cucumis, as traditionally circumscribed, was a genus of 25-30 species, predominantly distributed throughout tropical Africa. However, recent molecular studies have shown that its generic limits should be expanded: five smaller genera are now included in Cucumis and in this new circumscription it counts 52 species (Schäfer 2007; with identification key to all the species). Some of these are native to Asia and Australia. Several species are economically important, especially Cucumis melo (melon) and C. sativus (cucumber, gherkin). Both have been recorded as food refuse aliens in Belgium.
1 Pepos aculeate or echinate === 2
Pepos smooth === 3
2 Leaves deeply palmately lobed. Pepo short-ellipsoid to globose, 1.5–3(–5) × 1.5–3 cm, obscurely aculeate. Petiole with 3 different types of hairs in different zones. Tendrils antrorsely strigose === Cucumis myriocarpus
Leaves unlobed. Pepo ellipsoid to ellipsoid-cylindric or globose, 3.5–7 × 2.5–4 cm, densely echinate at maturity, obscuring fruit surface. Petiole with 1 type of hairs. Tendrils proximally hispidulous, distally glabrous === C. dipsaceus
3 Leaves 3-5-lobed, entire or shallowly lobed (leaf lobes obtuse). Fruit smooth (but densely hairy when young), usually spherical === C. melo
Leaves 5-7-lobed, angular (leaf lobes acute). Fruit tuberculate (especially when young), glabrous, usually cylindrical === C. sativus
Literature:
Ashurmetov O.A. (1995) On morphology and taxonomy of the genera Cucumis L. and Melo Mill. Feddes Repert. 106(3-4): 155-159.
Chung S.M., Staub J.E. & Chen J.F. (2006) Molecular phylogeny of Cucumis species as revealed by consensus chloroplast SSR marker length and sequence variation. Genome 49(3): 219-229.
De Wilde W.J.J.O. & Duyfjes B.E.E. (2007) The wild species of Cucumis L. (Cucurbitaceae) in South-East Asia. Adansonia 29(2): 239-248. [available online at: https://www.researchgate.net/publication/237329475_The_wild_species_of_Cucumis_L._%28Cucurbitaceae%29_in_South-East_Asia]
Garcia Mas J., Monforte A.J. & Arus P. (2004) Phylogenetic relationships among Cucumis species based on the ribosomal internal transcribed spacer sequence and microsatellite markers. Pl. Syst. Evol. 248(1-4): 191-203.
Ghebretinsae A.G., Thulin M. & Barber J.C. (2007) Nomenclatural changes in Cucumis (Cucurbitaceae). Novon 17(2): 176-178.
Jørgensen P.M. & Whitehouse C.M. (1997) Cucumis. In: Cullen J. & al. (eds.), The European Garden Flora, vol. 5. Cambridge University Press, Cambridge: 298.
Kirkbride J.H. (1993) Biosystematic monograph of the genus Cucumis (Cucurbitaceae): botanical identification of cucumbers and melons. Parkway Publishers, X + 159p.
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) Cucumis. In: Flora of North America Editorial Committee (eds.), Flora of North America North of Mexico, vol. 6. Oxford University Press, New York: 32-38. [available online at: http://www.efloras.org/florataxon.aspx?flora_id=1&taxon_id=108642]
Schaefer H. (2007) Cucumis (Cucurbitaceae) must include Cucumella, Dicoelospermum, Mukia, Myrmecosicyos, and Oreosyce: a recircumscription based on nuclear and plastid DNA data. Blumea 52: 166-177. [available online at: https://www.researchgate.net/publication/233659414_Cucumis_%28Cucurbitaceae%29_must_include_Cucumella_Dicoelospermum_Mukia_Myrmecosicyos_and_Oreosyce_a_recircumscription_based_on_nuclear_and_plastid_DNA_data]
Sebastian P., Schaefer H., Telford I.R.H. & Renner S.S. (2010) Cucumber (Cucumis sativus) and melon (C. melo) have numerous wild relatives in Asia and Australia, and the sister species of melon is from Australia. Proceedings of the National Academy of Sciences of the U.S.A. 107(32): 14269-14273. [available online at: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2922565/]
Singh A.K. & Yadava K.S. (1984) An analysis of interspecific hybrids and phylogenetic implications in Cucumis (Cucurbitaceae). Pl. Syst. Evol. 147(3-4): 237-252.
Staub J.E. & al. (1992) Phylogenetic relationships among several African Cucumis species. Canad. J. Bot. 70(3): 509-517.