The botanist's beard? (3)
I believe the answer is:
awn
'the botanist's beard?' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for awn that I've seen before include "Beard of plant" , "Beard growing from an ear of barley or rye" , "Bristly growth" , "Grass "beard"" , "Bristles" .)