A reproductive structure made up of a collection of sporangia. Sori are usually prominent on the undersurface of fertile fern fronds, where they are often borne in a regular pattern, each sorus being covered by an *indusium
. The reproductive areas, consisting of a mass of unilocular sporangia, found on the blades of the brown alga Laminaria are also termed sori as are the various spore-forming bodies of the rust fungi (e.g. the aecium, teleutosorus, and uredosorus).