Last object in front of flower (6)
I believe the answer is:
endure
'last' is the definition.
('endure' can be a synonym of 'last')
'object in front of flower' is the wordplay.
'object' becomes 'end' (I've seen this in other clues**).
'in front of' means one lot of letters go next to another.
'flower' becomes 'ure' (I have seen 'River of Wensleydale ' mean 'ure' so perhaps 'river' could also mean 'ure').
'end'+'ure'='ENDURE'
(Other definitions for endure that I've seen before include "Suffer, tolerate" , "brook" , "Last or undergo" , "Last (anag.)" , "Go through" .)