Desmidium is a genus of filamentous desmids that inhabit freshwater bodies and are common components of the surface material frequently referred to as “pond scum.” The hairlike strands are composed of short cells with deep constrictions and do not feature the spiny projections that may appear among other related genera. A prominent member of the genus is Desmidium swartzii, which is characterized by colonies of triangular cells 11 to 22 micrometers long and 24 to 39 micrometers wide. Since the individuals are connected in such a way that they twist slightly, the colonies of the species generally exhibit a spiraling shape.