Small reptile spotted on American plant (6)
I believe the answer is:
crocus
'plant' is the definition.
The answer is an example.
'small reptile spotted on american' is the wordplay.
'small reptile' becomes 'croc' (short for crocodile; 'small' suggests a short form).
'spotted on' means one lot of letters go next to another (in a down clue, some letters go on top of others).
'american' becomes 'us' (abbreviation for United States).
'croc'+'us'='CROCUS'
(Other definitions for crocus that I've seen before include "Flower from corm" , "it's ready for spring" , "Spring plant" , "Occurs (anagram)" , "Small plant with yellow, purple or white flowers" .)