A caryopsis is a small, one-celled, one-seeded, dry indehiscent fruit with the pericarp fused to the thin seed coat, the typical fruit of grasses and grains. The caryopsis is popularly called a grain and is the fruit typical of the family Poaceae (or Gramineae), which includes wheat, rice, and corn.

The term grain is also used in a more general sense as synonymous with cereal (as in "cereal grains"). Considering that the fruit wall and the seed are intimately fused into a single unit, and the caryopsis or grain is a dry fruit, little concern is given to technically separating the terms "fruit" and "seed" regarding the plant structures. All cereal grains except buckwheat will have caryopses.

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