Identification notes
At first sight, cushions of this acrocarpous moss, often growing on rocks by streams and rivers in the North and West, look a bit nondescript and spirits may fall at the unlikely prospect of a field identification. Maybe 1cm or so tall (sometimes a lot taller) with pale green spearhead shaped leaves curving away from the stem and with a stout nerve, it can seem hard to pick out any particularly distinctive feature. However, your investment in a good quality hand lens could pay off at this point – close examination of the leaf margin near the bluntish leaf-tip will usually reveal coarse teeth. This rules out most possibilities from such habitat, with the exception perhaps of Racomitrium aciculare, which can look similar when it tries. The leaf margins of this latter species, however, are clearly recurved up to and even beyond mid-leaf, whereas they are plane in Dichodontium.
A close relative is the less common D. flavescens. If capsules are present (unlikely), that of D. flavescens is erect, and 2-4 times as long as wide, whilst that of D. pellucidum is curved and 1-2 times a long as wide. Even without capsules, separating the two species is fairly reliable using leaf size and proportions: 4-5 times as long as wide in D. flavescens, 2.5 – 4 times in D. pellucidum. The longer, thinner leaves of D.flavescens can make it look a bit like Chionoloma tenuirostre which grows in similar habitats, but the leaves of that moss do not have the coarse teeth of the Dichodontium.
Interestingly, in the Shetland Islands, stunted D. pellucidum grows very commonly away from water, in cracks in the pavement, concrete by roadsides and other grotty places where you might expect Streblotrichum convolutum and can lead to confusion – the marginal teeth will of course pick out the Dichodontium.
Read the Field Guide account
