Plant needing hot, not primarily wet, external conditions (7)
I believe the answer is:
heather
'plant' is the definition.
(heather is a plant)
I don't understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for heather that I've seen before include "Lassie" , "Moorland flower" , "Small purple evergreen plant growing on hills" , "Small evergreen plant with purple flowers from highlands" , "Moorland flora" .)