In taxonomy, Ulothrix is a genus of algae, specifically of the Ulotrichaceae.Ulothrix is a genus of filamentous green algae, generally found in fresh and marine water. Its cells are normally as broad as they are long, and they thrive in the low temperatures of spring and winter. They become attached to surfaces by a modified holdfast cell. Reproduction is normally vegetative. They are Eukaryotic and unicellular. They are one of the 5 classes of microorganisms.