Plant growing on rocks right outside church (6)
I believe the answer is:
lichen
'plant growing on rocks' is the definition.
(I've seen this before)
'right outside church' is the wordplay.
'right' becomes 'lien' (legal right).
'outside' means one lot of letters goes inside another.
'church' becomes 'ch' (common abbreviation).
'lien' placed around 'ch' is 'LICHEN'.
(Other definitions for lichen that I've seen before include "Growth found on tree trunks and rocks" , "Simple plant often found growing on rocks" , "Tiny plants growing on rocks and treetrunks" , "Small plants found on tree-trunks and stones" , "It grows on rocks or bare ground" .)