Description: Thallus is a medium to dark green, unbranched, filament with a single file of cells (uniseriate), usually occurring in tangled skeins. Cells are cylindrical (75-150 mm diam.; 1-3 (- 5) times as long as wide), becoming only slightly barrel-shaped when fertile. Rhizoidal branches are usually lacking. Habitat: This species often forms dense, tangled mats that float around or snag on other seaweed in the mid to low intertidal in summer. Found in protected to semi-exposed habitats, tidepools, and mud flats. Similar taxa: Rhizoclonium spp. are narrower and generally prefer brackish habitats.