Plant, such a fine one, ruined (7)
I believe the answer is:
fuchsia
'plant' is the definition.
(type of shrub)
'such a fine one ruined' is the wordplay.
'fine' becomes 'f' (abbreviation e.g. condition of old coins, books).
'one' becomes 'i' (Roman numeral).
'ruined' is an anagram indicator.
'such'+'a'+'f'+'i'='suchafi'
'suchafi' anagrammed gives 'FUCHSIA'.
(Other definitions for fuchsia that I've seen before include "Ornamental garden shrub" , "Plant with drooping purple, red or white flowers" , "If such a plant is a showy flower" , "Purplish-red colour" , "Flower; colour" .)