Mean to change single plant (7)
I believe the answer is:
anemone
'plant' is the definition.
(anemone is a kind of plant)
'mean to change single' is the wordplay.
'to change' indicates an anagram.
'single' becomes 'one' (synonyms).
'mean' anagrammed gives 'anem'.
'anem'+'one'='ANEMONE'
(Other definitions for anemone that I've seen before include "bloomer" , "Brightly coloured flower or tube-shaped sea creature" , "Plant with bright flowers" , "Woodland plant - marine polyps" , "Flower; marine polyp" .)