Sicyos L.
Sicyos L., Sp. Pl. 2: 1013. 1753.
Type: Sicyos angulatus L., Herb. Clifford 452, Sicyos no. 1 (BM, Lectotype).

Sicyoides Mill., Gard. Dict. Abr. ed. 4. 1754.
Sechium P. Browne, Civ. Nat. Hist Jamaica 355.1756 (nom. cons.).
Bryoniastrum Heist. ex Fabr., Enum. 195. 1759.
Chayota Jacq., Select. Stirp. Amer. Hist. (ed. 1780 -1781) 124, t. 245. 1780.
Sicyosperma A. Gray, Smithsonian Contr. Knowl. 5: 62-63. 1853.
Sechiopsis Naudin, Ann. Sci. Nat., Bot., ser. 5, 6: 23-24. 1866.
Microsechium Naudin, Ann. Sci. Nat., Bot., ser. 5, 6: 25. 1866.
Pterosicyos Brandegee, Univ. Calif. Publ. Bot. 6: 72. 1914.
Ahzolia Standl. & Steyerm., Publ. Field Mus. Nat. Hist., Bot. Ser. 23: 92. 1944.
Anomalosicyos Gentry, Bull. Torrey Bot. Club 73: 565. 1946.
Sicyocaulis Wiggins, Madroño 20: 251. 1970.
Skottsbergiliana H. St. John, Pacific Sci. 28: 457. 1974.
Parasicyos Dieterle, Phytologia 32: 289. 1975.
Sicyocarya (A. Gray) H. St. John, Phytologia 38: 407. 1978.
Sarx H. St. John, Bot. Jahrb. Syst. 99: 491. 1978.
Cladocarpa (H. St. John) H. St. John, Bot. Jahrb. Syst. 99: 491. 1978.
Costarica L. D. Gómez, Phytologia 53: 97. 1983.

Annual or perennial climbers or trailers with up to 10 m long herbaceous shoots, fibrous to tuberous roots and monoecious sex system. The leaves are simple, petiolate (rarely sessile), with angulate or lobed blade. The tendrils are simple or (2-) 3-5 (-6)-fid, often with long stout peduncle. The flowers are small, white or yellowish-green. Male flowers are produced in racemes or panicles (rarely umbels), the female flowers solitary or in groups of 2-5 or in dense capitulae of up to 40. The receptacle-tube is (broadly) campanulate, in some species with pouch-like nectaries at the base. The five sepals ar dentiform to linear, very small. The corolla is rotate with five triangular to ovate-triangular, basally fused, rarely bifurcate petals. The 2-5 stamens are inserted near the base of the tube on filaments, which are fused into a central column. The anthers are all monothecous or two anthers bithecous and one monothecous, all anthers usually form a central head. The thecae are straight, duplicate, sigmoid or flexuous and contain 6-12-colpate, echinate, small to medium-sized pollen (polar axis 31-92 µm, equatorial axis 34-110 µm, (Khunwasi 1998)). The ovary is ovoid to fusiform, usually pubescent to setose, rarely winged or angular with solitary, pendent ovules. The styles are short or slender with (2-) 3 dilated, often reflexed stigmata. The fruits are dry or fleshy, indehiscent, solitary or clustered in capitulae, sometimes enclosed by a subtending leaf, small or medium-sized, globose, ovoid, obovoid, pear-shaped, fusiform, pedicellate, winged or 3-4 angled, armed with retrorse barbs or unarmed, glabrous or villous. The solitary seed is ovoid, tumid or compressed, sometimes germinating inside the fruit. The testa is smooth or crustaceous. The known chromosome numbers range from n = 12-15.

About 60-70 species growing on forest margins, hillsides, clearings, roadsides, pastures, and in seabird colonies, most from Mexico to Argentina, Hawaii, North America, Australia, New Zealand, Southwest Pacific (Islas Desventuradas), Galapagos (S. pentagonus, S. villosus) one species, S. polyacanthus in Africa (introduced). The chayote or xuxu, Sicyos edulis, is cultivated as a vegetable throughout the Tropics and Subtropics.

The genus Sicyos is placed in tribe Sicyeae (Schaefer et al. 2009, Schaefer & Renner 2011).

Literature

Carr, G. D. 1985. Additional chromosome numbers of Hawaiian flowering plants. Pacific Science. 39: 302-330.

Kearns, D. M., 1992. A revision of Sechiopsis (Cucurbitaceae). Syst. Bot. 17: 395-408.

Khunwasi, C. 1998. Palynology of the Cucurbitaceae. Doctoral Dissertation Naturwiss. Fak., University of Innsbruck.

Lira, R. and F. Chiang. 1992. Two new combinations in Sechium (Cucurbitaceae) from Central America and a new species from Oaxaca, Mexico. Novon 2: 227-231.

Mercado, P. and R. Lira. 1994. Contribution al conocimiento de los numeros chromosomicos de los generos Sechium P. Br. y Sicana Naudin (Cucurbitaceae). Acta Botanica Mexicana 27: 7-13.

Schaefer, H. and S.S. Renner. 2011. Phylogenetic relationships in the order Cucurbitales and a new classification of the gourd family (Cucurbitaceae). Taxon 60: 122-138.

Schaefer, H., Heibl, C., and S.S. Renner. 2009. Gourds afloat: a dated phylogeny reveals an Asian origin of the gourd family (Cucurbitaceae) and numerous oversea dispersal events. Proceedings of the Royal Society B 276: 843-851.