The oak genus, known as Quercus, contains a number of deciduous and evergreen hardwood trees in North America. Oak tree identification hinges on your ability to process information about an oak species that includes its size and the shapes of its leaves.
Other pertinent data that you must use to identify an oak tree pertains to the acorns, the bark and the habitat of the oak you encounter. Combining all of this can help you to understand what types of oaks you have growing in the ecosystems around you.
Oak trees can vary greatly in size, with some species themselves having wide fluctuations between their minimum and maximum heights. Some species, such as interior live oak, can be as tall as 80 feet, but are frequently no larger than a tall shrub. Other oaks typically grow to great heights, like the white oak, California Black oak and overcup oak, all of which can top 100 feet. Some of the smaller oaks species that stay in the range of around 50 feet tall include Chapman oak, chestnut oak and post oak.
The size and shape of oak leaves are among the best indicators of the species the tree belongs to. Some oaks have leaves with many lobes, with the lobes rounded. The number of lobes and the length of the leaf can help you recognize the tree. For instance, a bur oak has 6-to-12-inch-long leaves, as wide as 6 inches, which possess between five and nine rounded lobes. The leaves of Nuttall oak have five- or seven-pointed lobes tipped with small bristles and are from 4 to 8 inches long.
Oak tree bark can give you a clue to the tree's identity, especially when it has distinctive characteristics. Water oak, for instance, has bark that is a mottled combination of gray and black, with the bark broken into various scaly ridges, according to the "Trees of North America" guide. Bluejack oak has red-brown bark divided into small blocks that cover the trunk. Black bark with a series of deep ridges and furrows is a trait of silverleaf oak.
Oak trees produce a fruit known as acorns, with different species having acorns of various sizes and features. The length of the acorn can be a deciding factor in narrowing down a species. Some oaks have short acorns less than an inch long, like the shingle oak. Others have acorns well over two inches, with the California white oak a case in point. The cap of the acorn may play a role in oak tree identification. Some are very shallow, resembling saucers, like the caps on the acorns of Oregon white oak. Others encompass nearly the entire nut, such as overcup oak.
Certain oak species have a wide geographic range. These include the chinkapin oak, bur oak, white oak, black oak and blackjack oak---all oaks of the eastern United States. Other oaks exist in a much smaller area in distinct parts of the country. Such oaks are the Engelmann oak, emory oak and blue oak. Knowing what oaks grow native to where you live will quickly reduce the possibilities as to what oak a specific tree may be.