Cucurbitaceae
The Cucurbitaceae family only counts one native species in Belgium, Bryonia dioica Jacq. Many of the currently found alien representatives (except, for instance, Sicyos angulatus that is introduced unintentionally with grains) are probably food refuse casuals. They are most often found on dumps or sewage works, from discarded kitchen waste (more rarely also on river banks).
In addition to the species treated in detail in this account many more are cultivated for their edible fruits or as ornamentals (e.g. Cullen & al. 1997; Jäger & al. 2008). Grenfell (1984) provides a very useful illustrated overview with identification key for the British representatives of the cucurbit family.
Molecular phylogenetic studies within Cucurbitaceae family were recently conducted by Schaefer & Renner (2011). These authors also proposed a new infrafamilial classification.
1 Corolla whitish or greenish-white (never yellow or orangish). Fruit 6-15 mm in diameter. Pistillate flowers usually 2–16 === 2
Corolla yellow or orangish. Fruit variable in size but usually larger. Pistillate flowers usually solitary === 3
2 Corolla whitish. Fruit ca. 15 mm in diameter, covered with long setae. Tendrils branched. Monoecious annual. Leaves 5-lobed, lobes acute at apex. Stamens 5 === Sicyos
Corolla greenish-white. Fruit a red berry, 6-10 mm in diameter, never covered with setae. Tendrils simple. Dioecious perennial. Leaf lobes (sub-) obtuse at apex. Stamens 3 (native) === Bryonia
3 Corolla lobed halfway to base, 70-100 mm in diameter. Tendrils always branched === Cucurbita
Corolla lobed to base, 20-70 mm in diameter. Tendrils simple or branched === 4
4 Fruit echinate or aculeate === Cucumis p.p.
Fruit smooth === 5
5 Leaves deeply lobed, much more than halfway to base, the lobes again divided. Fruit very large, to 100 x 40 cm. Fruit pulp red. Tendrils simple or branched. Shoot apices woolly === Citrullus
Leaves shallowly lobed. Fruit pulp variable (if reddish, then fruit at most 4 x 2.5 cm). Tendrils simple. Shoot apices not woolly === 6
6 Leaves not lobed, cordate at base, with deep, suborbicular or semicircular sinus. Calyx segments reflexed, lanceolate, 12-13 × 2-3 mm. Male flowers solitary or clustered, 20-70 mm in diameter. Fruit 4 x 2.5 cm, red. Stamens 5 === Thladiantha
Leaves shallowly lobed, rarely entire, without deep semicircular sinus. Calyx segments subulate or linear, 2-4 × 0.4-1.2 mm. Male flowers clustered, ca. 20-25 mm in diameter (or less). Fruit very variable in shape and colour (but never red). Stamens 3 === Cucumis p.p.
Additional alien: Ecballium elaterium (L.) A. Rich. (syn.: Momordica elaterium L.) (Medit., Macar., W-As.).
Literature:
Given the economic importance of the Cucurbitaceae family, a vast and very divers literature is available. Only a selection of the more relevant references is provided hereunder and with the respective genus accounts.
Chrtková A. (1990) Cucurbitaceae. In : Hejný S. & Slavík B. (eds.), Květena České Republiky, vol. 2. Academia, Praha: 439-452.
Cogniaux A. (1916) Cucurbitaceae (Fevilleae et Melothrieae). In: Engler A. (ed.), Das Pflanzenreich 66. Engelmann, Leipzig: 1-277.
Cogniaux A. (1924) Cucurbitaceae (Cucurbiteae-Cucumerinae). In: Engler A. (ed.), Das Pflanzenreich 88. Engelmann, Leipzig: 1-246.
Cullen J. & al. (1997) The European Garden Flora, vol. 5. Cambridge University Press, Cambridge.
Grenfell A.L. (1984) Cucurbitaceae in Britain. BSBI News 38: 13-18. [available online at: http://archive.bsbi.org.uk/BSBINews38.pdf]
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.
Jeffrey C. (1962) Notes on Cucurbitaceae, including a proposed new classification of the family. Kew Bull. 15: 337-371.
Jeffrey C. (1966) On the classification of the Cucurbitaceae. Kew Bull. 20: 417-426.
Karlsson T. (2010) Cucurbitaceae. In: Jonsell B. (ed.), Flora Nordica, vol. 6: 70-78. The Swedish Museum of Natural History, Stockholm.
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) Cucurbitaceae. In: Flora of North America Editorial Committee (eds.), Flora of North America North of Mexico, vol. 6. Oxford University Press, New York: 3-58. [available online at: http://www.efloras.org/florataxon.aspx?flora_id=1&taxon_id=10233]
Renner S.S. & Pandey A. (2013) The Cucurbitaceae of India: Accepted names, synonyms, geographic distribution, and information on images and DNA sequences. Phytokeys 20: 53-118. [available online at: http://www.umsl.edu/~renners/Renner_Pandey_Indian_cucs_2013.pdf]
Schaefer H. & Renner S.S. (2011) Cucurbitaceae. Pp. 112-174. In: Kubitzki K. (ed.), Families and Genera of Flowering Plants, Vol. 10. Springer Verlag, Berlin.
Schaefer H. & Renner S.S. (2011) Phylogenetic relationships in the order Cucurbitales and a new classification of the gourd family (Cucurbitaceae). Taxon 60(1): 122-138. [available online at: http://www.umsl.edu/~renners/Schaefer&Renner_Cucs_Taxon2011.pdf]