Operculum (botany)

: opercula) or calyptra (from Ancient Greek καλύπτρα (kalúptra) 'veil') is a cap-like structure in some flowering plants, mosses, and fungi.

The operculum is formed by the fusion of sepals and/or petals and is usually shed as a single structure as the flower or fruit matures.

[2] In some species of monocotyledon, the operculum is an area of exine covering the pollen aperture.

[7] The sporangium of mosses usually opens when its operculum or "lid" falls off, exposing a ring of teeth that control the release of spores.

[8] There are two types of sexual spore-bearing asci of ascomycete fungi – those that have an operculum at the top of the ascus, and those that do not.