Darwin drops the odd beard (3)
I believe the answer is:
awn
'beard' is the definition.
(awn is a kind of beard)
I don't understand the rest of the clue.
Can you help me to learn more?
(Other definitions for awn that I've seen before include "bit of cereal" , "Bristle-like appendage on grass" , "Beard growing from an ear of barley or rye" , "Bristly head of barley sheath, quite wan" , "Beard of plant" .)