Collect short book on very famous plant expert (9)
I believe the answer is:
herbalist
'plant expert' is the definition.
'herbalist' can be an answer for 'expert' (herbalist is a kind of expert). I'm not sure about the 'plant' bit.
'collect short book on very famous' is the wordplay.
'collect short book' becomes 'herb' (I can't explain this - if you can you should believe this answer much more).
'on' is a charade indicator (letters next to each other).
'very famous' becomes 'a-list' (I've seen this before).
'herb'+'alist'='HERBALIST'
Can you help me to learn more?
(Other definitions for herbalist that I've seen before include "simple job" , "Early botanical writer" , "He dispenses simple cures" .)