Area covered by very good variety of tree (3)
I believe the answer is:
oak
'tree' is the definition.
(oak is a type of tree)
'area covered by very good variety' is the wordplay.
I cannot really see how this works, but
'area' could be 'a' (maths abbreviation) and 'a' is found in the answer.
'good' could be 'ok' and 'ok' is present in the remaining letters.
No letters remain.
This may be the basis of the clue (or it may be nonsense).
'of' acts as a link.
Can you help me to learn more?
(Other definitions for oak that I've seen before include "Its seed is the acorn" , "Acorns are its fruit" , "Hard durable wood of a deciduous tree" , "Nose of certain wines" , "From little acorns does it grow" .)