while in others (e.g. most Quercus), they are not. In Lithocarpus, the cupule is very hard and bone-like in texture.

The calybium is the fruit proper. It develops from an inferior ovary, meaning it is initially encased in the future cupule. Technically the calybium is a nut, as its ovary wall becomes dry with the embryo loosely enclosed inside, and remains closed until germination. In the