kalyptra

Kalyptra, often spelled calyptra, is a protective cap that covers the developing capsule (sporangium) of many moss sporophytes. It is formed from tissue associated with the archegonial region of the female gametophyte and initially envelopes the young sporangium. The calyptra helps protect the sporophyte from desiccation and physical damage during its development.

As the capsule matures, the calyptra typically withers or is shed, exposing the operculum through which spores are released. The timing of calyptra shedding and its persistence vary among moss species and can be a useful taxonomic character for identification. In some species the calyptra may remain attached longer or be only partially removed, while in others it is discarded early in capsule development.

In bryology, the presence, shape, size, pigmentation, and shedding pattern of the calyptra are notes of interest for describing and distinguishing moss taxa. The term derives from Greek roots meaning veil or covering, reflecting its protective role over the developing sporophyte. Kalyptra is the variant spelling used in some languages and texts.