The sori in ferns are groups of sporangia hanging on the underside of the leaves that attach to bumps on the leaf (so-called placentas). The different arrangement of the Sori on the leaf surface and the shape of the Sori are important determinants. Young Sori are often covered by so-called veils ( Indusia ).
Leaflets of the common fern with ripe sori in side view. The Indusia are crumpled, the individual sporangia (dark spheres) visible.
In mycology, various collections of spores are called Sori, such as the uredo- and teleutosporangia of the rust fungi or the burnt spore beds of the smut fungi (Ustilaginales) or the bare spore beds of the Acrasidae .