Mushrooms and toadstools (5)
I believe the answer is:
fungi
'mushrooms and toadstools' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for fungi that I've seen before include "Spore-producing organisms" , "Toadstools, say" , "Eg, toadstools" , "Yeasts, moulds, mushrooms etc" , "life in woodland?" .)