Wild flower trail expanded (3,4)
I believe the answer is:
dog rose
'wild flower' is the definition.
(I know that dog rose is a type of wild flower)
'trail expanded' is the wordplay.
'trail' becomes 'dog' (synonyms).
'expanded' becomes 'rose' (rise can mean to expand or grow).
'dog'+'rose'='DOG-ROSE'
(Other definitions for dog rose that I've seen before include "Flower of the hedgerow" , "wild shrub" , "something smelling nice in the hedgerow" , "bloomer" , "Hedgerow plant" .)