R. ellipticum is the only member of the genus (in Britain and Ireland at least) that forms small, neat cushions or tufts and has leaves without any hair-points (except perhaps for anomalous forms of R. sudeticum). It is one to search for in the mountains, where it can often be found on slabby, acidic rocks.
Without capsules it is puzzling plant which could be mistaken for a Grimmia, a Ulota or even an Orthotrichum. To check it is a Racomitrium, carefully pull an entire leaf from a stem and examine its base. R. ellipticum has hyaline basal marginal cells without sinuose walls restricted to 1-2 rows (see gallery image below).
Other good pointers for this species are its short, egg-shaped capsules and its dark, rather opaque leaves – because it is bistratose in the upper part of the leaf.Read the Field Guide account