Flower seen in odd places in The Fens (4)
I believe the answer is:
tees
'flower' is the definition.
(River Tees)
'odd places in the fens' is the wordplay.
'odd places in' means one should take alternating letters (letters in odd-numbered positions).
'the'+'fens'='thefens'
The alternating letters of 'thefens' are 'TEES'.
'seen in' acts as a link.
(Other definitions for tees that I've seen before include "English river" , "Current" , "River on which Middlesbrough stands" , "Starting places on the golf course" , "Northern river" .)