It grows on grass in lawns (3)
I believe the answer is:
awn
'it grows on grass' is the definition.
The definition suggests a singular noun which matches the answer.
'in lawns' is the wordplay.
'in' indicates the answer is hidden within the clue.
'AWN' is hidden in the letters of 'lawns'.
Can you help me to learn more?
(Other definitions for awn that I've seen before include "Bristle-like appendage on grass" , "Beard of plant" , "bit of cereal" , "Bristle in flowering part of some grasses" , "Bristle on grass spikelet" .)