| 1 | Cupule open and 2-16-lobed or completely enclosing the fruits; not dehiscent, or irregular so, or into 2-8 ± equal segments; always with vertical sutures. Nuts 1-15 in each cupule, rounded-angular or 2-3-gonous in cross-section. |
| 1' | Cupule never lobed, saucer-shaped, cup-shaped, or almost completely enclosing the fruit, indehiscent, without vertical sutures. Nut always solitary in a cupule, circular in cross-section. |
| 2 | Cupule lamellate or set with imbricate scales. Nuts 2-3-gonous in cross-section. Stigmas ligulate or capitate. |
| 2' | Cupule spiny, muricate, or rarely almost smooth. Nuts rounded-angular in cross-section. Stigmas punctiform, terminal. Leaves spirally arranged. Stipules not interpetiolar |
| 3 | Cupule solitary, axillary, lamellate, 2-lobed, containing 1-3 nuts. Fruits 2-gonous, winged. Stigmas ligulate. Leaves distichous, glandular-dotted. Stipules not interpetiolar, peltately attached |
| 3' | Cupules many along a rachis, scales imbricate to concentrically set; 4-16-lobed, containing 3-15 trigonous but not winged nuts. Stigmas capitate. Leaves in whorls of 3, not glandular-dotted. Stipules interpetiolar, not peltately inserted |
| 4 | Cupules solitary or in dichasial clusters, sometimes almost completely enclosing the fruit; variously squamose, muricate, or lamellate. Complete acorn without a ringed umbo. Stigmas punctiform. Leaves usually not crowded near the end of the branchlet, entire. Terminal buds solitary, scales imbricate |
| 4' | Cupules always solitary, saucer-shaped or cup-shaped, lamellate. Umbo of complete acorn ringed. Stigmas capitate. Leaves crowded at the end of the twig, entire or crenate in the apical half. Terminal buds conferted, scales with a tendency towards orthostichy |
