Normally, Racomitrium lanuginosum is a straightforward plant to identify in the field when it grows in upland habitats. Stunted forms may require examination under a high power microscope. There, it will be possible to recognise it as a Racomitrium by the basal cells of a leaf, which are linear, with sinuose-nodulose walls. The longitudinal walls are considerably thicker than the transverse walls.
Quite a few other species have obvious hyaline hairpoints, but only R. lanuginosum shows the combination of being coarsely and irregularly toothed, strongly papillose and longly decurrent down the leaf margins, as illustrated below.Read the Field Guide account