Plant river tavern in middle (7)
I believe the answer is:
rhubarb
'plant' is the definition.
(rhubarb plant is a kind of plant)
'river tavern in middle' is the wordplay.
'river' becomes 'r' (abbreviation for river).
'tavern' becomes 'bar' (I've seen this in another clue).
'in' means one lot of letters goes inside another.
'middle' becomes 'hub' (hub is a kind of middle).
'bar' going inside 'hub' is 'hubarb'.
'r'+'hubarb'='RHUBARB'
(Other definitions for rhubarb that I've seen before include "Red stalks" , "a word not meant to be understood" , "In America, heated dispute" , "Low-level racket" , "The pinkish stalks are edible, but the leaves are poisonous" .)