Plant releases iodine over area (7)
I believe the answer is:
freesia
'plant' is the definition.
(freesia is a kind of plant)
'releases iodine over area' is the wordplay.
'releases' becomes 'frees' ('free' can be a synonym of 'release'**).
'iodine' becomes 'i' (I is the chemical symbol for iodine).
'over' means one lot of letters go next to another.
'area' becomes 'a' (maths abbreviation).
'frees'+'i'+'a'='FREESIA'
(Other definitions for freesia that I've seen before include "Scented plant from South Africa" , "Sea rife with these odd flowers" , "Scented South African plant" , "Fragrant flower (sounds rather cold?)" , "Fragrant-flowered plant; faeries (anag.)" .)