1. A hood-shaped or cap-like structure covering the capsule of a moss.
Usage: botany; also spelled calypter
2. In botany, a cap-like covering or membrane on certain plant structures, such as the operculum of a flower bud.
Usage: technical; rare

Examples

• The calyptra of the moss fell away as the spore capsule matured.
• Botanists examined the calyptra under a microscope to identify the moss species.
• The delicate calyptra protected the developing sporangium.
• As the moss grew, the calyptra gradually detached from the capsule.