Although S. fimbriatum can look a little featureless, it is one of the few species of Sphagnum that can be reliably be identified without a microscope. The trick is to look for two important features – (i) a stellate capitulum topped by a large bud that sits above the branches and (ii) fimbriate stem leaves that are wider than tall and tattered across the apex and down the uppermost leaf margins too. Break off a capitulum to view the stem leaves at the top of the broken stem with a hand lens and you will probably see several overlapping each other and resembling a ruff as shown in the Gallery below.
This combination of prominent bud and wide, tattered stem leaves rules out all other similar-looking green species except Sphagnum girgensohnii, which is common only in the north and west of Britain. Examination of the stem leaves of that species will show them to be taller than wide and tattered only across the leaf apex.Read the Field Guide account