Plain green ties knotted (9)
I believe the answer is:
serengeti
'plain' is the definition.
(I've seen this before)
'green ties knotted' is the wordplay.
'knotted' indicates an anagram.
'green'+'ties'='greenties'
'greenties' with letters rearranged gives 'SERENGETI'.
(Other definitions for serengeti that I've seen before include "Tanzanian wildlife area" , "place to watch game" , "Green ties (anag.)" , "Tanzanian national park area" , "region in Tanzania" .)