Group of organisms, green sort (7)
I believe the answer is:
ecotype
'group of organisms' is the definition.
'green sort' is the wordplay.
'green' becomes 'eco' (abbreviation for ecological).
'sort' becomes 'type' (type is a kind of sort).
'eco'+'type'='ECOTYPE'
(Other definitions for ecotype that I've seen before include "Distinct species (in a particular habitat)" , "Organisms in a particular environment" , "One lives in a particular place" , "Subspecies adapted to particular environmental conditions" .)