Flowering plant, most unconfined, widely encountered (11)
I believe the answer is:
loosestrife
'flowering plant' is the definition.
'loosestrife' can be an answer for 'plant' (loosestrife is a kind of plant). I am not sure about the 'flowering' bit.
'most unconfined widely encountered' is the wordplay.
I cannot really understand how this works, but
'unconfined' could be 'loose' (synonyms) and 'loose' is found in the answer.
The remaining letters 'strife' is a valid word which might be clued in a way I don't understand.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for loosestrife that I've seen before include "Soil of trees (anag) -- waterside plant" , "Purple or yellow waterside plant" , "Primrose, say" .)