Microhabitat and morphometric variation in two species of Prasiola (Prasiolales, Chlorophyta) from streams in central Mexico

Prasiolales are characterized by high morphological plasticity. This problem in taxonomic delimitation of the species may be a result of environment heterogeneity. Habitat characteristics and morphological variation of P. mexicana and P. nevadensis, two species of freshwater leaf-like thallus green algae, were investigated in five sites in central Mexico where the morphological traits of these species overlap. Comparisons were made between habitat characteristics among streams and transects with and without Prasiola samples. Although no consistent correlation was found between environmental variables and morphological traits, a significantly wider range of habitat characteristics of current velocity and irradiance and morphometric variation (lamina length, lamina diameter, cell length, surface of the thallus, thickness and number of layers) suggested that P. mexicana was more plastic than P. nevadensis in its physicochemical requirements. Our results suggest that small variation of microhabitat conditions in P. nevadensis (irradiance and current velocity) could explain its very restricted geographic range in streams in central Mexico.