British distribution (genus): Widespread and common in freshwater.
Stigeoclonium is a common genus of freshwater algae in still and flowing waters, sometimes free-floating but more often attached to other plants or to hard surfaces. Usually there is a prostrate system, attached to the substrate and varying according to species, and from this arise the erect filaments. The filaments are usually branched and have short, lateral branches that end in an acute apex or hair-like extension, though the development of these multicellular "hairs" depends on nutrient limitation, particularly of phosphate. Each cell contains a single, parietal chloroplast (i.e. wrapped around the inner wall) and one to several pyrenoids.
John (in John et al., 2002) recognises nine British species but makes the point that the characters by which many have been recognised are now known to be influenced by the nutrient status of the water. Some "species" may simply be environmentally induced states of others.
Stigeoclonium species are tolerant of a wide range of water conditions, with some able to grow in waters polluted by heavy-metals and/or organic materials. S. tenue is probably the most common, certainly the most often reported, and it can be the dominant alga in nutrient-rich or polluted streams, e.g. those in heavy-metal mining areas.
The photographed material appeared in glass petri-dishes of nutrient-poor water taken from the edge of a peat-bog on Gleniffer Braes, Renfrewshire, April 2001. The erect filaments arose from rather disc-like attachments on the glass. The form of this attachment and the slender filaments with limited branching suggest the species is Stigeoclonium farctum Berthold, a common and variable alga, occurring usually in rivers, and not uncommonly colonising glass and plastic.