calyptra A protective cap- or hood-like covering on the developing capsule in a moss or liverwort. In mosses the calyptra usually remains until the capsule is almost ripe, when it usually falls. In liverworts the calyptra covers the capsule only very early in its development; later it may be visible as a collar at the base of the stalk.

calyptra
1. A layer of cells that covers the developing sporophyte of mosses, liverworts, clubmosses, horsetails, and ferns. In mosses it forms a hood over the capsule and in liverworts it forms a sheath at the base of the capsule stalk.

2. See root cap.