This common pleurocarp becomes conspicuous when its capsules mature between autumn and spring. Fortunately they are usually abundant as otherwise it is easily overlooked in its favoured habitats of stones on the woodland floor and wall tops.
Capsules are inclined, brown and ellipsoid with conical lids, and typical of species of Sciuro-hypnum, Brachythecium and Brachytheciastrum. The seta, like the majority of species in these genera, is deeply coloured and coarsely papillose. Its roughness is sometimes difficult to see with a hand-lens but becomes clear under a stereomicroscope.
S. populeum is more slender than its common relatives and differs from all except Brachytheciastrum velutinum in having long and narrow leaves with a drawn out tip which makes its shoots look quite wispy in the field. The nerve extends nearly all the way to the tip of the leaf, whereas in B. velutinum it peters out in mid-leaf. The leaves of that species are also a little wider and have a tendency to curve to one side, a character not seen in S. populeum.Read the Field Guide account