Operculum (botany)

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The flower buds of Eucalyptus erythrocorys have a large, bright red operculum.

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 (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.

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