Popular van Gogh painting (6)
I believe the answer is:
'popular van gogh painting' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for irises that I've seen before include "Subject for van Gogh" , "Expensive painting" , "Is sire in favour of flowers?" , "Coloured membranes in eyes, or showy flowers" , "blooms" .)