Filamentous Green Algae (Moss; Pond Scum)
Filamentous green algae forms green, cottony masses that are free-floating or attached to rocks, debris, or other plants. It consists of fine, green filaments that have no leaves, roots, stems, or flowers. They often form dense mats. On warm, sunny days, they commonly float when bubbles, generated by the plant or created by its decay, get trapped in the mats and make them buoyant. The three genera listed below are examples.
Cladophora feels cottony and can form balls that float when the core decays; magnification reveals long, slender cells and a branching habit.
Pithophora is sometimes called “horsehair algae” because of its coarse texture, which can feel like steel wool.
Spirogyra is bright green and slimy; magnification reveals the chlorophyll-bearing pigments are shaped as spirals; the filaments do not branch.
Note: Not all types of green algae are filamentous; they occur in an great variety of forms, including single cells and colonies.