In a heathland setting, there’s a good chance that a small, glossy-looking Bryum with red-orange spherical rhizoidal tubers might be B. bornholmense. B. rubens, with which it can be confused, is not normally a species of heaths or poor acid soils, preferring instead disturbed fertile basic to neutral soils.
The tubers of B. bornholmense are large, translucent and orange-red, with very thin-walled cells that are not very protuberant. As they are only borne on long rhizoids they never climb up the stems as those of B. rubens do. Also, tubers of B. rubens are crimson to dark red, opaque under transmitted light, and have protuberant cells with thicker walls. Watch out too for similarities to B. subapiculatum, which also likes acid soils.