Forest floor growth (4)
I believe the answer is:
moss
'forest floor growth' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for moss that I've seen before include "Stirling --, racing driver" , "Small flowerless green plant without proper roots" , "Small plants growing as thick mat" , "Type of plant growing in damp places" , "material not in Rolling Stones' collection?" .)