The sori are borne on the under surface of the pinnae, usually in a single row on either side of the midrib, but in Kaulfussia dotted over the expanded lamina.
The elongated receptacle of the marginal sori is surrounded by a basal cup-shaped indusium.
The sori, which are marginal, have a long receptacle, bearing the sporangia in basipetal succession, and are surrounded by a cup-shaped indusium.
The sori are developed in depressions and are thus protected within the resistent outer wall of the sporocarp. There are usually four sori in Pilularia, while in Marsilia they form two longitudinal rows.
If infection takes place, other sori are formed in ten days or a fortnight under favourable conditions of moisture and warmth.