Any ringlike anatomical part.

1. An elastic ring of cells between the operculum and the mouth of the capsule in mosses.

2. A line of cells, partly or entirely surrounding the sporangium in ferns, which constricts, thus causing rupture of the sporangium to release spores.

3. A whorl resembling a calyx at the base of the strobilus in certain horsetails.

The ringlike figure that lies between two concentric circles.

A ring of tissue representing the remnant of the veil around the stipe of some agarics.