Playwright Hart
I believe the answer is:
moss
'playwright hart' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for moss that I've seen before include "What's not found on a rolling stone" , "Stirling --, racing driver" , "Matted growth on trees, etc." , "English racing driver, b. 1929" , "Plant growing on many lawns" .)