Calla lily family
I believe the answer is:
'calla lily family' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for arum that I've seen before include "A sort of lily." , "genus of plants" , "Plant of the family Araceae, eg lords-and-ladies" , "A spirit for a lily" , "plant with a white spathe" .)