Cupule

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A cupule is a fruit structure found in flowering plants in the family Fagaceae. It holds and protects the nut during its growth and maturation. In some genera (e.g. Lithocarpus, Quercus), it only partly encloses the single nut, while in others (e.g. Castanea, Fagus), it fully encloses the two or more nuts, and splits open at maturity into four valves to release the nuts.

The cupule is covered by numerous scales. In some (e.g. Castanea), the scales are developed into sharp spines, giving the nut protection from squirrels and other seed predators, while in others (e.g. most Quercus), they are not. In Lithocarpus, the cupule is very hard and bone-like in texture.

The involucre is a similar structure found in the related family Betulaceae, notably in the genera Carpinus and Corylus; it differs in being more leafy in appearance, but performs a similar role in protecting the developing nuts. The term involucre is also used for similar structures in a number of other unrelated plant families.

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