Heather is a girl's name (5)
I believe the answer is:
erica
I believe this clue is a triple definition!
'heather' is the first definition.
(the plant genus Erica includes heather plants)
'is a girl's' is the second definition.
(I've seen this before)
'name' is the third definition.
(Other definitions for erica that I've seen before include "Female" , "Shrub genus; girl's name" , "Plant genus of garden heather" , "ling" , "Heather's Latin name?" .)