Valve morphology of Didymosphenia geminata (Bacillariophyceae) in Chubut Province, Argentina

Didymosphenia was recently found in Patagonia forming massive proliferations. In Argentina the species scattered in a short time to five provinces. Here, we analyse morphologic and morphometric data of specimens collected at Chubut Province, Argentina, and we compare them with other species of this genus reported from different regions of the world. Materials were collected in two basins during 2010-2012. Samples analyzed with LM and SEM showed inter and intrapopulation variation in morphometric characteristics and in some valve structures such as spines. The studied material corresponds in valve outline and morphology to D. geminata ssp geminata Metzeltin & Lange-Bertalot. Our materials also resemble a group of species: D. clavaherculis, D. clavamagna, D. coronata and D. laticollis. The studied material can be easily confused to some specimens mentioned in the literature as D. clavaherculis but they clearly differ from the type material of the species. On the other hand, fine morphology of the studied materials coincides with materials from Chile. Although morphological revision of the genus recently published allowed separating many species, there are still doubts about specific limits of taxa closely related to D. geminata. Molecular analysis should be performed to clarify these issues.