calyptra

noun

1. In bryophytes, a thin hood of tissue that forms from the archegonium and covers the developing sporophyte and is shed as it ripens.

   “(b) sporophyte with foot reduced, the entire sporophyte enveloped by the calyptra, which is ± stipitate at the base.”

2. any cap-like covering of a flower or fruit, such as the operculum over the unopened buds of Eucalyptus flowers
3. Any of various coverings at the tips of structures, in the terminology of various authors; for example rootcaps and the apical cells of trichomes.
4. In flies such as the housefly, Musca, in the taxonomic order Diptera, zoological section Schizophora, subsection Calyptrata, the calyptra is a membranous rearward extension of the forewing; it covers the haltere.