Absolute recognition is assured by presence of the unique acorns and their cups.
Most oaks have a deeply penetrating taproot.
Pith usually 5-angled, bundle scars in the leaf scars about 12 and difficult to count, stipules small and early deciduous, leaving inconspicuous scars. Leaves all petioled. Flowers unisexual, appearing before or as leaves develop, both sexes on the same plant. Stigmas 3-lobed, the ovules 6. All 38 are included in the key that follows.