Small quantity of grasses, mostly rudimentary (8)
I believe the answer is:
inchoate
'rudimentary' is the definition.
(both can mean still in development)
'small quantity of grasses mostly' is the wordplay.
I cannot quite see how this works, but
'quantity' could be 'inch' (inch is a kind of quantity) and 'inch' is located in the answer.
'of' could be 'o' and 'o' is present in the answer.
The remaining letters 'ate' is a valid word which might be clued in a way I don't see.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for inchoate that I've seen before include "Immature" , "Imperfectly formed" , "just beginning" , "Unfinished" , "Undeveloped" .)