Older bryologists may remember the days when S. capillifolium was a broad species concept that included S. rubellum, now a species in its own right. Although there can be a little overlap in identification characters, the two species are normally distinct enough not to be confused with each other.
Until you’ve pressed your hand on a (peat-forming) hummock of S. capillifolium and felt its firm resistance, you may find it difficult to visualise what the books say about its habit. In these hummocks, the individual shoots are pressed tightly together and each convex capitulum (think baseball cap as a mnemonic for capillifolium) resembles a small reddish cauliflower. If in any doubt, check the stem leaves – they are larger than S. rubellum and a different shape.Read the Field Guide account