Flowers: one comes up (6)
I believe the answer is:
irises
'flowers' is the definition.
(I've seen this before)
'one comes up' is the wordplay.
'one' becomes 'i' (Roman numeral**).
'comes up' becomes 'rises' (rising is a kind of coming up).
'i'+'rises'='IRISES'
(Other definitions for irises that I've seen before include "Eye membranes or showy flowers." , "Is sire in favour of flowers?" , "Subject for van Gogh" , "Coloured membranes in eyes, or showy flowers" , "Flowers found in the eye" .)