Quercus
Inflorescence appearing with the leaves in spring; sterile catkins from terminal or lateral buds on shoots of the preceding year, bracted, usually several in a cluster, unbranched, long, cylindrical, pendulous; bracts of sterile flowers minute, soon falling; calyx parted or lobed; stamens 3-12, undivided: fertile flowers terminal or axillary upon the new shoots, single or few-clustered, bracted, erect; involucre scaly, becoming the cupule or cup around the lower part of the acorn; ovary 3-celled; stigma 3-lobed.
White Oaks
Leaves with obtuse or rounded lobes or teeth; cup-scales thickened or knobbed at base; stigmas sessile or nearly so; fruit maturing the first year.
Black Oaks
Leaves with pointed or bristle-tipped lobes and teeth; cup-scales flat; stigmas on spreading styles; fruit maturing the second year.