Based on studies of herbarium collections, fieldwork in Mexico and Central America, and palynological evidence, two species of Frantzia (F. panamensis and F. venosa) are transferred to Sechium, and a species in this genus (S. chinantlense) from the lowlands of Oaxaca is described as new. A key to the 10 species of Sechium is presented. According to the most recent classification of the Cucurbitaceae (Jeffrey, 1990), the genus Sechium P. Browne belongs to tribe Sicyeae, subtribe Sicyinae. Ever since Jeffrey's (1978) work, in which a broader generic circumscription of Sechium was presented (encompassing Ahzolia Standley & Steyerm., Frantzia Pittier, and Polakowskia Pittier), there has been a growing interest in the genus. CruzLeon (1985-1986) and Cruz-Le6n & Querol-Lipcovich (1985) reported wild populations of S. edule (Jacq.) Sw. found in 1982-1983 in Veracruz, Mexico. Newstrom (1985, 1986, 1989, 1990, 1991) presented the results of her research on the origin and evolution of this species, reporting new localities for wild populations of the species in Oaxaca, Mexico, and proposing a different generic circumscription. Studies of collections (including type material) of all species of Sechium and related genera, fieldwork in Mexico and Central America (Lira, 1990, 1991; Lira & Soto, 1991), and palynological studies of species of most of the genera of subtribe Sicyinae (Lira & Alvarado, 1991) have revealed new evidence supporting Jeffrey's (1978) generic circumscription. Taking into account all the above-mentioned works, we propose two new combinations and a new species of Sechium. Sechium panamense (Wunderlin) Lira & Chiang, comb. nov. Basionym: Frantzia panamensis Wunderlin, Bull. Torrey Bot. Club 104: 102. 1977. TYPE: Panama. Chiriqui: Boquete District, Bajo Chorro, 6,000 ft., Davidson 416 (holotype, F, photograph). Geographical distribution. Apparently endemic to Panama, known only from the type locality, at elevations between 1,800 and 3,000 m. Additional specimens examined. PANAMA. CHIRIQUI: top of peak between Baru and Respinga, ca. 3,000 m, 27 Nov. 1975, D'Arcy 10135 (MO); Cerro Pata de Macho, ca. 5 mi. NE of Boquete, trail to continental divide leading to Finca Serrano (Francisco Serrano, Pacific slope), 22 Nov. 1979, Antonio 2687 (MO); Bugaba, Cerro Punta, along ridge to watershed to Bocas del Toro, 8?52'N, 82033'W, 2,200 m, 26 Jan. 1985, van der Werff& Herrera 6458 (MO). Sechium venosum (L. D. Gomez) Lira & Chiang, comb. nov. Basionym: Frantzia venosa L. D. Gomez, Phytologia 53: 447. 1983. TYPE: Costa Rica. Lim6n: along road from Hone Creek to Bribri, Gomez et al. 20483 (holotype, MO; isotypes, BM, CR, K). Geographical distribution. Originally reported (G6mez & Gomez, 1983) as endemic to the lowlands of Caribbean Costa Rica, it has now been found at higher elevations (1,300-1,650 m) and also in Pan-