Part of speech in French introducing a garden plant (7)
I believe the answer is:
verbena
'garden plant' is the definition.
(I've seen this before)
'part of speech in french introducing a' is the wordplay.
'part of speech' becomes 'verb' (verb is a kind of part of speech in grammar).
'in french' becomes 'en' (French word for 'in').
'introducing' is a charade indicator (letters next to each other) (some letters go before others).
'verb'+'en'+'a'='VERBENA'
(Other definitions for verbena that I've seen before include "Garden plant" , "Herbaceous plant" , "Vervain (plant)" , "Ornamental plant with showy flowers" , "Ornamental pant" .)