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Phormidium A genus of filamentous, sheathed cyanobacteria (section III) in which the sheaths tend to coalesce. They are capable of gliding motility (see MOTILE). They are found in all types of aquatic environment, and on wet rocks, damp soil, etc., often forming dense mats. They are frequently difficult to distinguish from Lyngbya and Plectonema (the LPP group).