Most luxuriant (7)
I believe the answer is:
lushest
'most luxuriant' is the definition.
('lush' can be a synonym of 'luxuriant')
This is the entire clue.
(Other definitions for lushest that I've seen before include "Most luxurious in growth" , "Most profuse or succulent" , "Most luxuriant" , "Most juicy" , "Most fleshy" .)