Ulothrix flacca

Mermaid's tresses

Authority: (Dillwyn) Thuret

Thallus is composed of unbranched filaments with a single file of cells (uniseriate) to 6 cm (~2.4 in) in length. The filaments usually appear coalesced and dark green on rock. The cells have a single nucleus, and although narrow (14-33 μm diameter), they are shorter (5-15 μm long) than wide. The single collar-shaped chloroplast fills the length of the cell but not the full circumference. Reproductive cells swell in the middle to 50 μm diameter.