Riparian forests are known to be a favorable environment for the establishment of Orchidaceae, however, difference in altitudinal gradient and changes in environmental conditions affect species diversity. This study aimed to investigate the composition and distribution of Orchidaceae occurrence in a riparian forest of the river Canhada Funda in Pouso Novo, Rio Grande do Sul. Five sampling points were marked along the stream and the species where sampled by the "Caminhamento" method. With measures of dissimilarity and clustering analysis the floristic similarity between the points was verified and the relation between species richness and altitud was verified by Pearson's linear correlation. Thirty six (36) species and 23 genera were inventoried, being Gomesa (5), Acianthera (4) and Cyclopogon (4) the most representative. The greatest diversity of orchids was observed at elevations below 300 m were vegetation was more preserved. It is believed that the composition and distribution of Orchidaceae in the area was influenced mainly by the altitudinal gradient and the conservation conditions of the riparian forest.
riparian forest; altitudinal gradient; degradation gradient; floristic similarity