Perennial plant (4)
(Other definitions for iris that I've seen before include "Flowers in the eye?" , "Coloured part of the lamp" , "- - Murdoch, novelist" , "In the middle of which pupil is opening" , "may open up in camera" .)
(Other definitions for lily that I've seen before include "Flower, maybe of the valley" , "Eg, arum, calla" , "Tiger -; water -" , "Fragrant flower" , "Bulb with showy, typically pendulous flowers" .)
(Other definitions for dahlia that I've seen before include "Flower, often ball-shaped" , "Ali had (anag) - showy flower" , "Showy bloom" , "Large-headed flower" , "Flower genus" .)