Rose I exchanged for willow (5)
I believe the answer is:
osier
'for willow' is the definition.
(osier is a kind of willow)
'rose i exchanged' is the wordplay.
'exchanged' indicates an anagram.
'rose'+'i'='rosei'
'rosei' is an anagram of 'OSIER'.
(Other definitions for osier that I've seen before include "Willow used in weaving" , "Tree - Rosie (anag)" , "growing in a bed" , "Basket material" , "Wood" .)