DEA agent is suspicious one's a plant (9)
I believe the answer is:
narcissus
'a plant' is the definition.
The answer is an example.
'dea agent is suspicious one's' is the wordplay.
'dea agent' becomes 'narc' (I've seen this in another clue).
'is suspicious one's' becomes 'issus' (I can't justify this - if you can you should believe this answer much more).
'narc'+'issus'='NARCISSUS'
Can you help me to learn more?
(Other definitions for narcissus that I've seen before include "Spring flower" , "Small daffodil" , "Spring-flowering bulb" , "Garden flower - youth of Greek mythology" , "Flower; Gk. youth in love with reflection" .)