British distribution (genus): Widespread, freshwater and marine.
The gametophyte (shown here) is a filamentous, usually unbranched green alga, characterised by its ring- or band-like chloroplasts with one to several pyrenoids. Filaments may be free-floating in small pools but are more often attached by a basal cell to stones and boulders in streams and on rocky shores, or mat-forming in saltmarshes, depending on species.
The sporophyte (not shown) is unicellular.
Photograph of unnamed species in culture, 1998.