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An operculum or (in plural) opercula are botanical terms describing a certain structure or structures of certain vascular plants, mosses, or fungi which act as a cap, flap, or lid. In vascular plants, an operculum may also be called a bud cap.
Examples of structures identified as opercula include:
- A flap of the sporangium of a moss, covering the peristome (appendages surrounding the mouth of a moss capsule).
- The cap of the ascus in certain ascomycetous fungi.
- A lid covering the aperture of pollen grains.
- The bud cap covering the flowers of Eucalyptus and Corymbia trees which falls off as they open.
- The covering of a pyxidium (fruit capsule whose upper part falls off when the seeds are released) of a plant, such as the plantain.
- The flared leaflet that prevents a pitcher plant from accumulating rainwater.