Perigynium

In botany, a perigynium (plural: perigynia), also referred to as a utricle, typically refers to a sac that surrounds the achene of plants in the genus Carex (Cyperaceae). The perigynium is a modified prophyll, also known as a glume, which is tissue of leaf origin that encloses the dry, one-seeded achene.

In liverworts, "perigynium" refers to a tube-shaped structure which encases the archegonium and the developing sporophyte.

The location, size, shape, hairiness, color, and other aspects of the perigynium are important structures for distinguishing Carex species. They are often subtended by a scale, which may also aid in identification.