Common groups of species initially leaving (7)
I believe the answer is:
general
'common' is the definition.
(I've seen this before)
'groups of species initially leaving' is the wordplay.
'groups of species' becomes 'genera' (I've seen this before).
'initially' says to take the initial letters.
The first letter of 'leaving' is 'l'.
'genera'+'l'='GENERAL'
(Other definitions for general that I've seen before include "Opposite of private!" , "Enlarge (anag.)" , "Not specialised, like army chief" , "Rank; normal, usual" , "Not specialised, rank" .)