Plants flag endlessly around Oregon (5)
I believe the answer is:
flora
'plants' is the definition.
(I've seen this before)
'flag endlessly around oregon' is the wordplay.
'endlessly' means to remove the last letter.
'around' indicates putting letters inside.
'oregon' becomes 'or'.
'flag' with its last letter taken off is 'fla'.
'fla' going around 'or' is 'FLORA'.
(Other definitions for flora that I've seen before include "Various plants" , "Botanical specimens" , "local plants" , "Plant life of particular area" , "list of plant life" .)