Heather genus (5)
I believe the answer is:
erica
'heather genus' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for erica that I've seen before include "hardy shrub" , "Plant of the heath genus" , "Moorland plant, girl's name" , "Heather, for instance" , "growing up on the moors" .)