Fungus shape (5)
I believe the answer is:
mould
I believe this clue is a double definition.
'fungus' is the first definition.
(I know that mould is a type of fungus)
'shape' is the second definition.
(I know that shape can be written as mould)
(Other definitions for mould that I've seen before include "Cast; form" , "Crumbly soil" , "development of earth" , "Furry fungus" , "Cause of discoloration" .)