Unties best raised plant (7)
I believe the answer is:
freesia
'plant' is the definition.
The answer is an example.
'unties best raised' is the wordplay.
'unties' becomes 'frees' (I've seen this in another clue).
'best' becomes 'ai' (resembles 'A1', old-fashioned term for excellent).
'raised' says the letters should be written backwards (going up in a down clue).
'ai' back-to-front is 'ia'.
'frees'+'ia'='FREESIA'
(Other definitions for freesia that I've seen before include "Scented plant from South Africa" , "bloomer" , "Fragrant flower (sounds rather cold?)" , "Highly scented flower" , "Fragrant-flowered plant; faeries (anag.)" .)