Queen introduced to geum as a garden plant (8)
I believe the answer is:
geranium
'a garden plant' is the definition.
(I've seen this before)
'queen introduced to geum' is the wordplay.
'queen' becomes 'rani' (historical term for a Hindu queen).
'introduced to' is an insertion indicator.
'rani' inserted inside 'geum' is 'GERANIUM'.
'as' acts as a link.
(Other definitions for geranium that I've seen before include "Commonly cultivated plant" , "Cultivated flower often seen in window box" , "Run image of the flower" , "Cultivated cranesbill" , "Flower for a strange Maine rug" .)