Plant article to fill a space like this (10)
I believe the answer is:
agapanthus
'plant' is the definition.
(agapanthus is a plant genus)
'article to fill a space like this' is the wordplay.
'article' becomes 'an' (indefinite article).
'to fill' means one lot of letters goes inside another.
'space' becomes 'gap' (gap is a kind of space).
'like this' becomes 'thus' (I've seen this before).
'a'+'gap'+'thus'='agapthus'
'an' put within 'agapthus' is 'AGAPANTHUS'.
(Other definitions for agapanthus that I've seen before include "flower" , "Bloomer" , "garden plant" , "Flowers" , "Southern African plant of the lily family -- haunts a gap (anag)" .)