Survey and distribution of Batrachospermaceae (Rhodophyta) in tropical, high-altitude streams from central Mexico

Freshwater Rhodophyta populations from high altitude streams (1,725-2,900 m a.s.l.) in the Mexican Volcanic Belt (MVB), between 18-19° N and 96-100° W, were investigated through the sampling of six stream segments from 1982 to 2006. Three species are documented, Batrachospermum gelatinosum, B. helminthosum and Sirodotia suecica, including their descriptions and physical and chemical water quality data from their environment. Batachospermum helminthosum and S. suecica are reported for the second time in MVB streams, with a first description in detail for the freshwater red algal flora from Mexico. All species were found in tropical climates (two seasons along a year, dry and rainy), at high altitudes (> 1,700 m a.s.l.), mild water temperatures (9.0-20.4°C), circumneutral (pH 6.0-8.2, bicarbonate as the dominant anion), and with a relative low ionic content (salinity 0.1 to 0.2 g l^-1, specific conductance 77-270 μS cm^-1). Two ecological groups of species were clearly distinguished on the basis of nutrient content. The first group, which includes B. helminthosum, is characterized by clean waters with low nutrient concentration, while the other, with B. gelatinosum and S. suecica, thrive surprisingly well in nutrient-rich waters. The overall species composition for streams in the MVB revealed strong similarities with freshwater red algal floras from other temperate regions in North America and other continents.