Identification notes

A scarce moss but one that, given ideal conditions, can be locally abundant. Its presence often indicates a likelihood of finding other scarce riparian bryophytes nearby, for example Fissidens polyphyllus, Porella pinnata and Heterocladium wulfsbergii.

R. alopecuroides typically grows submerged or semi-submerged much of the time, on rocks in fast-flowing base-poor watercourses. It has a particular liking for cascades and waterfalls and in any given watercourse may be confined to any such features. Unless water levels are low enough to expose its substrate, R. alopecuroides is easily overlooked.

Although its ubiquitous relative, P. riparioides, also grows in watercourses, they seldom co-exist. R. alopecuroides requires base-poor, clean water whereas R. riparioides is most common in eutrophic, base-rich water and is also relatively pollution tolerant. Sometimes R. alopecuroides will live in the upper parts of a river, being replaced by R. riparioides downriver as water chemistry changes due to geology and water entering from tributary streams.

Any doubt between the two species is readily dispelled by measuring the width of the mid-leaf cells under a microscope.

Distribution in Great Britain and Ireland

Capsules, thought to be rare except in north Wales, appear to be increasingly found in populations in south-west England.