In all, over thirty taxa of algae were identified in Taylor Valley streams. To allow for finer distinctions to be made concerning physical characteristics, species belonging to the family Oscillatoriaceae were divided into thirteen distinct morphotypes. These morphotypes were defined based on the following characteristics: trichome width, cell length, presence or absence of a calyptra (thickened membrane on the terminal cell, occurrence or otherwise of numerous trichomes within a common sheath, and shape of the apical cell. Each morphotype was then assigned to the species that most closely matched its description. In many cases, more than one morphotype was assigned to a single species. Morphotype L consisted of trichomes less than 2.5 micrometers in width, making them very difficult to distinguish at x400 magnification. As a result, two species of Oscillatoriales (Phormidium frigidum and Oscillatoria deflexa) were assigned to this particular morphotype.