Identifying Oak Species
Behold the breadth of the oak family. There are approximately 600 individual species listed in the Quercus (Oak) genus--most are trees, though a few are shrubs. Some are deciduous, some evergreen, some semi-evergreen. Oaks are mostly native to woodlands in the Northern Hemisphere, but they vary widely, from cold and temperate forests across North America and Europe to the tropical jungles of Asia and Central America. Some evergreen oak trees (particularly certain American Species) are commonly called "Live Oak". This grouping name describes several species with an evergreen growth pattern, and it does not reflect any taxonomic classification group--in some cases, these species are only distantly related. Thus, evergreen oaks (Live Oaks) can be considered as a type of oak tree, but only insofar as they're an evergreen oak variety.
Understand which oak species grow in your region. Find an illustrated field identification guide to take with you to the woods; pictures will help you immensely in your quest to name specific species of oak. In North America, oak trees are split into two main groups: "red oak" and "white oak". Red oaks tend to have darker bark, and lobed leaves that come to a point; white oaks tend to have lighter bark, and leaves with rounded lobes. Common "white oak" species include chinkapin oak (found in limestone-rich soils), live oak, blackjack oak (found on dry ridges), shingle oak (found on moist slopes), swamp chestnut oak (found in wetlands), white oak (found in various ecosystems), swamp white oak (found in wetlands), and overcup oak (found on stream-banks, in marshy bottomlands). Common "red oak" species include water oak (found near stream-banks and lowlands), northern red oak (found in various habitats), southern red oak (found on moist and dry slopes), scarlet oak (found on dry slopes), willow oak (found on moist slopes), pin oak (found in wetlands), and cherrybark oak (found near moist slopes and bottomlands).
Identifying Oak Leaves
Learn to identify oak leaves. Look for a "lobe and sinus" pattern on the oak leaves--the blades of the leaf and the indentations in between. The lobes of the leaf are the rounded and pointed protrusions that give the leaf its shape. Think of these lobes like "leaf fingers", or extensions of the stem. Different species of oak may have either pointed or rounded lobes. Red oaks tend to have pointed lobes, and white oaks tend to have rounded lobes. Between each lobe is a sinus, which is an indentation in the leaf that accentuates the lobes. Sinuses may be variably deep, shallow, wide, or narrow. Evergreen species can have leaves that are ‘entire’ (without lobes or teeth) or that have only faintly wavy edges.
Look closely. Oak leaf shapes can vary across a single tree. You may need to inspect a number of leaves to make an accurate classification. If you can't tell the species from the leaves alone, consider other characteristics, such as the acorn, the bark, and the location--both in terms of terrain and geographic location. Oak leaves grow in a spiral pattern along the branch, meaning that a fan of leaves will rarely appear "flat" or parallel in the way that, say, palm fronds grow. Oak branches tend to divert from a straight line, and they do not have opposing growth on the branches: imagine that you're looking at a fork with multiple branches originating in the same place.
Look for green leaves in summer, red leaves in fall, and brown leaves in winter. Most oak tree leaves sport a deep green hue during the summer months, but transform into red and brown colors for the fall. Acorns are another telltale sign of oak trees. The oak tree is one of the most colorful fall trees, which is another reason they are popular in many types of landscaping today. Some oak leaves also emerge in a red or pink shade in early spring, but quickly change to their standard green color by summer. Oaks tend to lose their leaves late in the season, and younger trees or branches will hold their dead brown leaves all the way into spring. They will begin to fall when new leaves start to grow in the spring. A telltale sign of an oak in the winter is a tree with dead brown leaves. Oak leaves have a longer decay rate and will stay around longer than most other leaves. You can usually find them near the base of an oak tree, but be careful, as leaves can blow around on a windy day.
Use the fall foliage to tell between red and white oaks. White oak species may yield reddish-brown leaves when autumn comes, but red oaks tend to boast the most dramatic fall foliage. Red oak leaves turn to a deep, rich red which bursts out boldly from the late-autumn forest. Red oaks are often mistaken for maples. Maples tend to show their fall colors earlier in the season, and they've mostly exhausted their pigment by the time the oak foliage comes into full swing. You can also tell maples by their large, distinctive leaves.
Identifying Acorns
Understand the function of the acorn. The acorn contains the "seeds" of the oak tree, and an acorn buried in the right location may eventually sprout into a towering oak in its own right. The acorn develops within a cup-like structure called a cupule. The cupule delivers the nutrients that flow from the roots and leaves all through the tree, along the branches, and through the stem into the acorn. When the acorn rests with its point facing down, the cupule should look like a sort of cap atop the nut. The cap is not a part of the acorn, technically, so much as a protective covering. Each acorn typically contains one oak seed, although the occasional nut contains two or three. An acorn takes 6 to 18 months to mature into a sprouting oak seedling; acorns sprout best in a moist (but not too moist) environment, and their growth is naturally activated by the cold-snap temperatures of a Northern Hemisphere winter. Acorns have evolved to be deliciously appealing to deer, squirrels, and other woodland creatures. When animals eat the acorns that litter the forest floor, they take tiny oak seeds on board. When they excrete the digested acorn seeds--or, in the case of squirrels, compulsively hide acorns and then forget about them in the springtime--they spread the oak's seeds throughout their ecosystem. Most seeds do not survive to become full-fledged oak trees, but the ones that do survive eventually begin to produce acorns of their own. When an acorn falls to the ground, it has roughly a 1 in 10,000 chance of becoming a full-fledged oak tree--so you can imagine why it behooves the oak to produce so many!
Look for acorns on branches or around the base of the tree. Acorns may vary in size and color, but most are characterized by a bumpy "cap" and a smooth, pointed bottom. The following measurements may help you gather information about a tree: Observe the stem on which the acorn grows. Notice the length of the stem and how many acorns grow from it. Note the appearance of the cupule. The nut of the acorn grows from a woody cup, which may remind you of a head wearing a hat. Cupules may be scaly and include wart-like hairy growths which may take the form of a fringe, or may be characterized by color changes such as concentric rings.
Measure the length and diameter of the nut. Some species have long nuts, while others are fat and almost spherical. Measure how much of the acorn the cupule covers. As a general rule, full-grown red oak acorns are slightly larger: 3/4 to 1 inch long, with the cupule covering about 1/4 of the nut. Full-grown white oak acorns tend to be slightly smaller: 1/2 to 3/4 inch long.
Note the characteristics of the acorns. Note the color of the nut, whether it has a pointed end, and whether it has any other distinguishing features like ridges or stripes. Red oak acorns tend to take on a rich reddish-brown color, while white oak acorns tend to favor pale-gray hues. White oak species produce acorns on a one year cycle; these acorns contain fewer tannins and taste better to the woodland creatures--deer, birds, and rodents--that eat them, but they are more sporadic from year to year in acorn production. Red oak species take two years to mature an acorn, but they reproduce yearly, and they commonly provide a reliable crop on a yearly early basis. Although the red oak acorns contain more tannins and, in theory, don't "taste as good", this doesn't seem to deter woodland creatures from gobbling any acorns they can find. Red oak acorns usually contain large amounts of fats and carbs, but white oak acorns contain the highest carb content.
Identifying Oak Wood and Bark
Consider the bark. Look for hard, grey, scaly bark with deep grooves and ridges. The ridges and furrows often mingle with flattened gray areas on the larger branches and the main trunk. The color of the bark may fluctuate somewhat between oak species, but is is nearly always a shade of gray. Some oak bark is very dark, approaching black, and some bark is nearly white.
Consider the size of the tree. Old-growth oaks, particularly, are distinctive for their impressive size, and in some areas (such as California's "golden hills") these behemoths dominate the landscape. Oak trees tend to grow fairly large and round, with some reaching heights of 100 feet (30.5 m) or more. Oak trees are full and balanced, and it is not uncommon for an oak's width (including branches and foliage) to match its height. Oak trunks can be massively thick: some species commonly boast a girth of 30 feet (9.1 m) or more. Oak trees can live for more than 200 years--some have been known to live for more than 1000 years. For the most part, the thicker the trunk, the older the tree. The canopy of the oak tree tends to be relatively broad, which makes this tree a popular provider of shade and privacy during the summer months.
Identify oak wood once it's been cut. If a tree has been felled, cut, and split, you may need to consider characteristics like the color, the smell, and the look of the grain. Oak is one of the hardest trees, which is why its wood is a popular choice for furniture, flooring and other household amenities. Dry oak logs are prized as firewood, as they burn slowly and thoroughly. Again, there are many species of oak, so it helps to know where the tree was felled. If you don't know where the wood came from, you may only be able to tell whether you're dealing with red or white oak. This knowledge should suffice for most non-scientific purposes. Red oak wood will have a red tint and will dry to a slightly deeper red. White oak wood will be lighter in color. Oak wood is often mixed up with maple, but you can distinguish the two by their scent. Maple has a sweeter smell--hence maple sugar--and oak has a heavier, smokier smell.
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