Distribution patterns of ferns and lycophytes in the Coastal Region of the state of Rio Grande do Sul, Brazil

A survey of ferns and lycophytes of the Coastal Region of the state of Rio Grande do Sul (CRRS) was performed based on field work and collections of the main regional herbaria. The following were evaluated for each species: preferential habits (terrestrial, epiphytic or aquatic), geographic distribution patterns and habitats (forest, grassland, and wetland). The occurrence of a latitudinal gradient in diversity was tested over five latitudinal ranges using the Sørensen Similarity Index. A total of 17 lycophyte and 206 fern species representing 28 families was found between the latitudes of 29° and 34°S. Exclusively terrestrial species were predominant (162), with the majority (113) exhibiting wide Neotropical distributions, followed by species that also occurred in the state of Paraná (44). The forest habitat harbored the greatest number of species (159), while grasslands had the fewest (26). Cluster analysis showed pronounced floristic differentiation among latitudinal Ranges III (31°01' to 32°S) and IV (32°01' to 31°S), with a similarity index of only 0.41. Our results demonstrate a strong north-to-south reduction in species richness in the study area, which is related to environmental conditions along the latitudinal gradient and, especially, microclimatic differences in the transition zone between the Atlantic Forest and Pampa biomes.