In this work, we propose the new combination Stuckenia punensis (Galan de Mera) Galan de Mera for use in the Peruvian flora. This species is coincident with S. filiformis in its distribution in the high Andes of Peru. Stuckenia punensis differs from S. filiformis in its wider, scabrous leaves and globose achenes. On account of the recent revision of the worldwide genus Potamogeton L. (Wiegleb & Kaplan, 1998), we elucidate some points regarding the family Potamogetonaceae in South America. Recent articles on Potamogetonaceae in America include Standley and Steyermark (1958), Haynes (1974), Haynes and Wentz (1975), Haynes and Holm-Nielsen (1982), Tur (1982), Haynes (1985), and Galan de Mera (1991). After reviewing the nomenclatural novelties of Les and Haynes (1996) and Haynes et al. (1998), we propose an additional new combination of Stuckenia for the Peruvian flora. Stuckenia punensis (Galdn de Mera) Galdn de Mera, comb. nov. Basionym: Potamogeton punense Galdn de Mera, Phytologia 64: 495. 1988. TYPE: Peru. Puno: Lampa (on San Roman border), at road and railroad crossing of stream draining lago Jaracocha, ca. 9 km SW of Santa Lucia, 12 Jan. 1963, alt. ca. 4000 m, H. H. & C. M. Iltis 1441, D. & V Ugent (holotype, USM; isotype, US). Although Wiegleb and Kaplan (1998) suggested that Potamogeton punense and R filiformis C. H. Persoon [Stuckenia filiformis (C. H. Persoon) C. Bdrner] are synonymous, the two species are very different in their morphological and ecological characteristics (see Table 1). Stuckenia punensis presents much wider leaves, with 3 to 5 nerves, thickened and scabrous. The leaves of S. filiformis are narrower, with only 1 nerve, and smooth. The stipules of S. punensis are longer (5-8 cm) than those of S. filiformis (1-3 cm). The achenes also differentiate the two species: in S. punensis they are globose and in S. filiformis they are gibbous. Both species are located between 3000 and 4000 m above sea level, but their ecological preferences are different; whereas S. punensis lives in flowing rivers, S. filiformis forms dense communities in high calm lagoons. Finally, S. punensis is a Peruvian endemic (Galdn de Mera, 1991), while S. filiformis is widely distributed throughout the world (western, central and northern Asia, North and South America) (Wiegleb & Kaplan, 1998). Additional specimens of Stuckenia punensis. PERU. Cuzco: Calca, bottom of rio Urubamba Valley at km 54, on road to Urubamba, ca. 4 km NW from Calca (8 km SE of Yucay), 2900 m, 26 Dec. 1962, H. H. & C. M. Iltis, C. Vargas 846 (US, USM). Junin: Tarma, bottom of rio Quishuarcancha, below Hacienda Casa Blanca (ca. 18 km (air) SSE of Tarma), 3600 m, 28 Nov. 1962, H. H. & C. M. Iltis, D. & V Ugent 140 (USM); Yauli, aquatics from icy-cold, shallow, swift rio Mantaro, in limestone valley with treeless tussock, grassland along highway to Junin, ca. 8-10 km NW of La Oroya, ca. 3800 m, 4 Dec. 1962, Hugh H. & Carolyn Iltis, Donald & Vivian Ugent s.n. (US, USM); cerca de Paccha, entre La Oroya y Junin, Riachuelo, 3800-3900 m, 10 Jan. 1949, Ramdn Ferreyra 5259 (US). Table 1. A comparison of Stuckenia punensis and S. filiformis. Feature S. punensis S. filiformis Leaf width (mm) 2-4 0.2-0.5 Number of leaf 3 to 5 1