Prince holds member of insurgency which is growing in the country (8)
I believe the answer is:
harebell
'prince holds member of insurgency which is growing in the country' is the definition.
The definition and answer can be both plants as well as being singular nouns.
Maybe there's an association between them I don't understand?
'prince holds member of insurgency' is the wordplay.
'prince' becomes 'hal' (Shakespearean nickname of Henry V when a prince).
'holds' means one lot of letters goes inside another.
'member of insurgency' becomes 'rebel' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'hal' placed around 'rebel' is 'HAREBELL'.
Can you help me to learn more?
(Other definitions for harebell that I've seen before include "Delicate blue campanula" , "Blue wild flower -- beer hall (anag)" , "Minor bloomer" , "One to blossom" , "Pale blue flower in beer hall, oddly" .)