Division of leaf on large heart of speciality plant (7)
I believe the answer is:
lobelia
'plant' is the definition.
(lobelia is a kind of plant)
'division of leaf on large heart of speciality' is the wordplay.
'division of leaf' becomes 'lobe'.
'on' means one lot of letters go next to another.
'large' becomes 'l'.
'heart of' indicates the central letters.
The middle letters of 'speciality' are 'ia'.
'lobe'+'l'+'ia'='LOBELIA'
(Other definitions for lobelia that I've seen before include "Lo, I bale out the flower" , "Flower used for hanging baskets" , "Oilable (anag)" , "One of the bellflower family grown as a bedding plant" , "something flowery" .)