Difficulty over what sounds like a dwarf plant (7)
I believe the answer is:
burdock
'plant' is the definition.
The answer is an example.
'difficulty over what sounds like a dwarf' is the wordplay.
'difficulty' becomes 'rub' (rub is a kind of difficulty).
'over' is a reversal indicator.
'what sounds like' shows a homophone (sound like).
'a dwarf' becomes 'doc' (one of the seven).
'doc' sounds like 'dock'.
'rub' written backwards gives 'bur'.
'bur'+'dock'='BURDOCK'
(Other definitions for burdock that I've seen before include "Plant with sticky seed cases" , "Dub rock (anag.)" , "Wild plant" .)