Taxonomy and distribution of freshwater Blennothrix ganeshii Watanabe et KomArek (Oscillatoriaceae, Cyanophyceae) from central Mexico

Abstract

The genus Blennothrix belongs to the family Oscillatoriaceae (subfamily Oscillatorioideae), differing from others in the subfamily by the presence of several trichomes in a sheath. Freshwater members of Blennothrix have been recently divided into eight species (Komarek 1998), with the taxon B. ganeshii Watanabe et Komarek reported from three sites in two tropical basins of the central region of Mexico. However, information on anatomical (vegetative and reproductive) characters and environmental distribution is scarce and species determination is uncertain. This study analyses the anatomical structure of Blennothrix populations distributed in different sites along the central tropical region of Mexico in order to determine the taxonomic status of the studied populations. Eight populations were sampled, with concurrent environmental data recorded. Morphological characters previously considered to be of taxonomic importance, as well as complementary features such as algal mat length, filament diameter, trichome width, length of cells, and thickness and shape of the sheath were measured in several filaments of each sample. Our results showed that all the observed populations in the central region of Mexico fit within the circumscription of B. ganeshii (Watanabe & Komarek 1989, Komarek 1998). However, two important morphological features were observed in all populations. First, branches were rarely present and varying in frequency from 1 to 3 trichomes per filament. Second, the presence of a transverse lamellation due to constriction in the longitudinal axis of the sheath was observed. Some morphological characters described for this species were extended.