Bitter root, extremely coarse leaves (4)
I believe the answer is:
sour
'bitter' is the definition.
(I've seen this before)
'root extremely coarse leaves' is the wordplay.
I cannot really see how this works, but
'extremely' could be 'so' ('so' can mean 'extremely' or 'very') and 'so' is found in the answer.
The remaining letters 'ur' is a valid word which might be clued in a way I don't understand.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for sour that I've seen before include "Tasting sharp like stale milk" , "Disparagement of something one can't have oneself" , "Sharp- or tart-tasting" , "Acid or caustic" , "Acid - rancid" .)