Fruit matures in 1 season. The inner surface of the shell is glabrous and the seed is sweet.
Wood is often with tyloses.
Range extends throughout the Northern Hemisphere.
Fruit generally matures in 2 seasons. The inner surface of the shell is generally tomentose and the seed is generally bitter.
Wood is often without tyloses.
Range is restricted to North America.
2. Leaves are more or less deeply lobed - 3
3. Eastern species - eastern white oaks
4. Leaves often entire; usually oblong to lanceolate - willow oaks
5. Eastern species - eastern red oaks
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Approximately 500-600 species (with many more varieties) distributed throughout the temperate regions of the Northern Hemisphere and extending to the tropics at higher elevations. They are the most important hardwood genus in North America. There are approximately 60 species in the U.S. which are generally intermediate in tolerance. Twigs are relatively stout with stellate pith and clustered buds at the end of the twig.
Subgenera
White Oaks
Leaves are deciduous or persistent and usually have lobes without bristle tips.
Leaves are deciduous or persistent, usually with bristle-tipped lobes or bristles on margins and occasionally are entire.
Groups of Quercus
1. Leaves generally with bristle-tipped lobes or bristles on margin - red or black oaks - 4
2. Leaves coarsely or sinuately toothed or shallowly lobed or entire - chestnut oaks
3. Western species - western white oaks
4. Leaves usually pinnately lobed or broadly obovate and lobed at apex - 5
5. Western species - western red oaks