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New Discoveries of Gnetum in Tropical America

1965; Missouri Botanical Garden; Volume: 52; Issue: 3 Linguagem: Inglês

10.2307/2394800

2162-4372

Fr. Markgraf,

Geology and Paleoclimatology Research

As yet the peculiar gymnospermous genus Gnetum in the New World is only known by six species in the Amazon Basin and in the Guyana Highland.These species are differently distributed: 1) G. urens (Aubl.)Bl. follows the coastal rain forest from the lower Orinoco River (Catalina) to south of the lower Amazon River (Braganga); 2) G. nodiflorum Brongn.inhabits savannahs and wood edges in the Guyana Highland from its eastern border up to the Rio Negro in Venezuela, and similar situations of the Terra Firme in the Amazon region; 3) G. paniculatum Spruce is rarer in the Guyana Highland and runs from its eastern border to its southern border, following the Rio Negro valley; 4) G. venosum Spruce is found only in the rain forest of the lower and middle Amazon River up to Manaos; 5) G. Schwackeanum Taub.has a similar distribution, but seems to extend a little farther up the right tributaries (Rio Madeira, Rio Acre); 6) G. Leyboldii Tul. is bound to the wet rain forests, even swampy igapo forest, in the real lowlands along the whole Amazon River, stopping at the tributaries below the rapids (cachoeiras).By the kindness of several American herbaria specimens of this genus came under my eyes, collected in Panama, and thus extending considerably the area of the genus.Of course now the question arises, where their affinities are to be sought.Morphologically, they stand forth by large, often almost orbicular leaves shining silk-like on the upper surface by means of a dense subepidermal layer of fibres parallel to the secondary nerves.Inflorescences, flowers and fruits those of G. Leyboldii Tul.; now this species is Amazonian.But the large geographical gap is bridged over by a discovery made by Oscar Haught 1 in 1935 in the valley of Rio Magdalena in western Colombia.This sample agrees completely with those from Panama.In the meantime, Swedish botanists, E. Asplund and F. Fagerlind with G. Wibom, have discovered the genus Gnetum even in Ecuador 2 and R. E. Schultes with G. A. Black and J. Cabrera also in southwestern Colombia.They found two species, G. nodiflorum Brongn.and G. Leyboldii Tul.In Ecuador the species reach the district of Tunguragua, in Colombia that of Rio Uaupes.On the eastern slope of the Andes, they ascend a little higher up together with the rain forest (to about 250 m above sea level); as maximum altitude Asplund fixed 1200 m on Rio Pastaza.Both species however stop at the lower part of that eastern slope.The taxon of the Rio Magdalena remains separated by the Eastern Cordillera.By this segregation its morphological differentiation from the similar Amazonian G. Leyboldii may well correspon 1 His samples were named by Killip as Gnetum colombianum on the herbarium sheets, but this name seems to have never been published.2 An old-mentioned species of Ecuador, Gnetum trinerve Spruce (Notes of a botanist in the Amazon and Andes 2 (1908) 279)), according to its type specimen at Kew has proved to be a Loranthacea described by Trelease as the type of his Phoradendron trisulcatum (Trelease, the genus Phoradendron (1916) 155).