A type of moss (8)
I believe the answer is:
sphagnum
'a type of moss' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for sphagnum that I've seen before include "Pale peat moss -- human GPs (anag)" , "Occupant of bogs" , "Kind of moss that grows on bogs" , "Bog moss" , "Peat moss plant" .)