Jack-in-the-pulpit (4)
I believe the answer is:
arum
'jack-in-the-pulpit' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for arum that I've seen before include "Type of plant, lily perhaps" , "Perennial" , "Plant with small flowers and arrow-shaped leaves - kind of lily" , "Type of 1 Across" , "Plant of the family Araceae, eg lords-and-ladies" .)