An opening? A nithead like that flowering South African plant? (10)
I believe the answer is:
agapanthus
'flowering south african plant?' is the definition.
'agapanthus' can be an answer for 'plant?' (agapanthus is a plant genus). I'm unsure of the 'flowering south african' bit.
'an opening? a nithead like that' is the wordplay.
'an' becomes 'a'.
'opening?' becomes 'gap' ('gap' can be a synonym of 'opening').
'nithead' becomes 'n' (head letter of 'nit').
'like that' becomes 'thus' (I've seen this before).
'a'+'gap'+'a'+'n'+'thus'='AGAPANTHUS'
Can you help me to learn more?
(Other definitions for agapanthus that I've seen before include "Flowers" , "Southern African plant of the lily family -- haunts a gap (anag)" , "Bloomer" , "flower" , "garden plant" .)