British distribution (genus): Widespread.
14 species are recognised in the British Isles by Johnson (in John et al., 2002), their identification depending on reproductive features. The related genus, Zygnemopsis, with two British species, both rare, also cannot be distinguished from Zygnema when only vegetative. Many of the species have broad ecological requirements, occuring in ponds, streams, ditches and similar waterbodies, often forming extensive 'blanket weed' growth. Z. stellinum is given as a fairly common species in ditches and in moorland pools.
Photograph of material in culture, 1998, species unnamed.
Related genera include Spirogyra and Mougeotia. The systematic position of the conjugating green algae has been questioned, with some authorities moving them out of the phylum Chlorophyta.