noun
- A membranous covering or flap that protects the developing sporangia (spore cases) in ferns.
Usage: botany; also called indusia (plural)
Examples
- The indusium of the fern unfolds as the sporangia mature.
- Botanists examine the shape and position of the indusium to identify fern species.
- Under the microscope, the delicate indusium protects the spore-producing structures.
- The indusia on the underside of fern fronds vary in form among different species.