Bouquets not initially containing river plants (6)
I believe the answer is:
osiers
'plants' is the definition.
The answer is an example.
'bouquets not initially containing river' is the wordplay.
'bouquets' becomes 'posies' ('posy' can be a synonym of 'bouquet').
'not initially' means to remove the first letter.
'containing' is an insertion indicator.
'river' becomes 'r'.
'posies' with its first letter taken off is 'osies'.
'osies' going around 'r' is 'OSIERS'.
(Other definitions for osiers that I've seen before include "Kind of willows for weaving - Rosie's?" , "Roses I find with flexible willow twigs" , "Flexible twigs used in basketwork" , "Willow twigs used in basket-work" , "Small willows" .)