Perennial reptilian superpower (6)
I believe the answer is:
crocus
'perennial' is the definition.
(crocus is a perennial flower)
'reptilian superpower' is the wordplay.
'reptilian' becomes 'croc' (short for crocodile).
'superpower' becomes 'US' (the United States is a global superpower).
'croc'+'us'='CROCUS'
(Other definitions for crocus that I've seen before include "Flower from corm" , "Bulbous plant with brilliant coloured flowers" , "Plant from a corm" , "Spring bulb" , "Small pretty spring flower, yellow or white" .)