American reptile started on flower (6)
I believe the answer is:
crocus
'flower' is the definition.
(I've seen this before)
'american reptile started' is the wordplay.
'american' becomes 'US' (abbreviation for United States).
'reptile' becomes 'croc' (short for crocodile).
'started' is a charade indicator (letters next to each other).
'us' put after 'croc' is 'CROCUS'.
'on' is the link.
(Other definitions for crocus that I've seen before include "Slow transition" , "'Spring flower, source of saffron (6)'" , "Small pretty spring flower, yellow or white" , "Small plant with yellow, purple or white flowers" , "Flower from corm" .)