Cucumis

Plants annual [perennial], usually monoecious, rarely dioecious (C. anguria) or andromonoecious (C. melo), procumbent, trailing, or climbing; stems annual, hispid to hirsute; roots woody or thin [rarely tuberous]; tendrils usually unbranched, rarely unbranched and 2-branched or absent. Leaves: blade ovate, palmately 3–6[–7]-lobed or unlobed, lobes triangular or elliptic, oblong, ovate, obovate, or spatulate, margins serrate or entire, surfaces eglandular. Inflorescences: staminate flowers solitary or 2–10(–18) in axillary racemes, fascicles, or panicles; pistillate flowers usually solitary, rarely 2 or 3 in fascicles, from different axils than staminate, peduncles straight in fruit; bracts absent [rarely present]. Flowers unisexual (rarely gynecandrous in C. metuliferus); hypanthium infundibular to campanulate, 2–10 mm; sepals (4–)5, straight, linear to oblong or narrowly to broadly triangular; petals 5, distinct or basally connate, yellow, elliptic to ovate or obovate, 2–25[–37] mm, glabrous or pubescent, corolla campanulate to infundibular (constricted distally into a neck). Staminate flowers: stamens 3; filaments inserted near hypanthium base, distinct; thecae distinct, oblong, replicate (usually 2-folded) [straight to arcuate], connective broadened; pistillodes absent. Pistillate flowers: ovary 3–5-locular, ovoid to ellipsoid; ovules 15–150 per locule; style 1, short-columnar; stigmas 1, sublobate to 3-lobed, lobes sometimes with 1–9 fingerlike projections on margins; staminodes present or rarely absent. Fruits pepos, mono- or bicolor, green to yellow, orange, or tan [white, brown, purple] with light or dark green, white, yellow, brown, or orange [purple] longitudinal stripes, usually ellipsoid, globose, or cylindric, rarely obovoid [ovoid, rarely spindle-shaped], smooth, glabrous, surfaces densely echinate, or aculeate to muricate, sometimes netted, warty, scaly, or ridged, indehiscent. Seeds 50–500, ellipsoid to ovoid, compressed, not arillate, margins not differentiated, surface smooth. x = 12.

Distribution

Asia (China, India, Indonesia, Malaysia), Africa, Atlantic Islands (Cape Verde Islands), Indian Ocean Islands (Aldabra, Madagascar, Seychelles), Pacific Islands (Philippines), Australia, also introduced nearly worldwide.

Discussion

Species ca. 55 (6 in the flora).

Two Cucumis species are major commercial vegetable crops––C. melo, the melons (cantaloupes, honeydew, muskmelons, sugar melon, winter melon) and C. sativus, the garden cucumber. Cucumis anguria (the West Indian gherkin) and C. metuliferus (the kiwano) also are used commercially.

Most Cucumis plants in the flora area are escapes from gardens, trash dumps, or picnic discards and do not persist long outside cultivation. The dudaim melon (C. melo), paddy melon (C. myriocarpus), and a few others possibly have the potential to become aggressively invasive.

C. Jeffrey (1980b) recognized Cucumis subg. Cucumis (comprising two species, C. sativus and the closely similar C. hystrix Chakravarty) and subg. Melo (Miller) C. Jeffrey. Infrageneric classification has been modified by L. W. D. van Raamsdonk et al. (1989) and J. H. Kirkbride (1993), and based on insights from molecular data, H. Schaefer (2007) divided the genus into two subgenera, subg. Cucumis (50 species in five sections) and subg. Humifructus H. Schaefer (two species).

C. Jeffrey (1990) circumscribed the subtribe Cucumerinae (tribe Melothriae) to include Cucumis and five smaller genera––Cucumella, Dicoelospermum, Mukia, Myrmecosicyos, and Oreosyce. Molecular studies (A. G. Ghebretinsae et al. 2007; H. Schaefer 2007) indicate that Cucumis is paraphyletic without the 19 species of these five genera, and Schaefer formally broadened Cucumis to include them.

An Asian origin has been demonstrated for both Cucumis melo and C. sativus by P. Sebastian et al. (2010), using data from plastid and nuclear DNA. The wild progenitor of C. melo occurs in India and its sister species is C. picrocarpus F. Mueller from Australia. The closest relative of C. sativus is C. hystrix Chakravarty from the eastern Himalayas. The Asian/Australian Cucumis clade comprises at least 25 species.

The sister genus to Cucumis is Muellerargia Cogniaux, with one species in Madagascar (M. jeffreyana Keraudren) and one in Indonesia and Australia (M. timorensis Cogniaux). Both are in African/Asian clades that include the genera Coccinia Wight & Arnott, Neoachmandra de Wilde & Duyfjes, Peponium Engler, and Zehneria Endlicher (S. S. Renner and H. Schaefer 2008).

Cucumis sativus (subg. Cucumis) is the only species of the genus reported to have a chromosome number of 2n = 14; the only other species of subg. Cucumis (fide J. H. Kirkbride 1993), C. hystrix, has been reported to have a number of 2n = 24 (Chen J. F. et al. 1997). All Dysploid numbers of 2n = 20 and 2n = 22 have been reported from C. melo, which otherwise has 2n = 24. The chromosome number of Muellerargia has not been reported.

Most of the 52 species of Cucumis in the sense of Jeffrey are monoecious perennials, and key difference in Cucumis, and the mode of fruit opening also are much more evolutionarily labile than formerly thought (for details see S. S. Renner et al. 2007).

The monograph by J. H. Kirkbride (1993) has been a primary source in preparing this treatment.

Selected References

Boone, N.C. Naudin, C. V. 1859. Essais d’une monographie des espèces et des variétés du genre Cucumis. Ann. Sci. Nat., Bot., sér. 4, 11: 5–87.

Chung, S. M., J. E. Staub, and J. F. Chen. 2006. Molecular phylogeny of Cucumis species as revealed by consensus chloroplast SSR marker length and sequence variation. Genome 49: 219–229.

Ghebretinsae, A. G., M. Thulin, and J. C. Barber. 2007. Relationships of cucumbers and melons unraveled: Molecular phylogenetics of Cucumis and related genera (Benincaseae, Cucurbitaceae). Amer. J. Bot. 94: 1256–1266.

Kirkbride, J. H. 1993. Biosystematic Monograph of the Genus Cucumis (Cucurbitaceae): Botanical Identification of Cucumbers and Melons.

Raamsdonk, L. W. D. van, A. P. M. Nijs, and M. C. Jongerius. 1989. Meiotic analyses of Cucumis hybrids and an evolutionary evaluation of the genus Cucumis. Pl. Syst. Evol. 163: 133–146.

Renner, S. S. and H. Schaefer. 2008. Phylogenetics of Cucumis (Cucurbitaceae) as understood in 2008. In: M. Pitrat, ed. 2008. Cucurbitaceae 2008: Proceedings of the IXth EUCARPIA meeting on Genetics

Lower Taxa

Cucumis anguria, Cucumis dipsaceus, Cucumis melo, Cucumis metuliferus, Cucumis myriocarpus, Cucumis sativus

Key

1	Pepos netted, ridged, scaly, smooth, or warty	> 2
1	Pepos aculeate, echinate, or muricate (sometimes obscurely in C. anguria)	> 3
2	Leaf lobes triangular; staminate flowers: corolla tube 3.5–5(–6) mm; pistillate flowers: corolla tube 3.5–6.5 mm.	Cucumis sativus
2	Leaf lobes elliptic or oblong to ovate; staminate flowers: corolla tube 0.8–2 mm; pistillate flowers: corolla tube 1–1.6(–3) mm.	Cucumis melo
3	Plants dioecious; pedicels of pistillate flowers distally dilated; staminate flowers 3–10 in racemes.	Cucumis anguria
3	Plants monoecious; pedicels of pistillate flowers not distally dilated; staminate flowers 1–7, usually in fascicles or panicles, rarely racemes	> 4
4	Tendrils antrorsely strigose; petioles proximally retrorsely strigose, medially hirsute, distally antrorsely strigose.	Cucumis myriocarpus
4	Tendrils glabrate to hispid or proximally hispidulous, distally glabrous; petioles setose or weakly hispidulous to hispid	> 5
5	Petioles setose; pistillate flowers: calyx lobes 2–3 mm, corolla lobes sparsely puberulent inside; pepo surface muricate to aculeate; rootstock woody.	Cucumis metuliferus
5	Petioles weakly hispidulous to hispid; pistillate flowers: calyx lobes 5–6(–11) mm, corolla lobes glabrous inside; pepo surface densely echinate; rootstock not woody.	Cucumis dipsaceus