Identify the oak tree by its size. The largest oaks are the white oak (Q. alba), which grows 80 to 150 feet tall with a 3- to 5-foot trunk diameter; the swamp red oak (Q. pagoda), which reaches 100 to 130 feet tall with a 3- to 5-foot trunk diameter; and the Willow oak (Q. phellos), which grows 80 to 130 feet tall with a 3- to 6-foot-diameter trunk. The smallest are the bluejack oak (Q. incana), a small, shrubby tree that's less than 30 feet tall with a short, irregular trunk, and the Chinkapin oak (Q. muehlenbergii), also shrub-like and grows 10- to 30 feet tall.
Spot the Florida oak tree by studying its leaves. For example, the bluff oak (Q. austrina) has oblong, three-lobed leaves that are yellow-green and can vary in size. The Chapman oak (Q. chapmanii) has narrow, non-lobed leaves that are silvery-green and 3½ inches long. The myrtle oak (Q. myrtifolia) has small evergreen leaves that are only 1 to 2 inches long, oval, non-lobed and with spiny tips and smooth margins. The post oak (Q. stellata) has cross-like leaves with two central lobes that are slightly square and larger than the rest. They have a dark green upper surfaces with short, fine, soft hairs and wooly undersides.
Study the trees' branches and crown. The live oak (Q. virginiana) has a broad, buttressed trunk base and low-growing, massive, wide-spreading branches. The laurel oak (Q. laurifolia) has slender branches forming a broad, dense and round canopy. The overcup oak (Q. lyrata) is a smaller tree with crooked, twisted branches. The water oak (Q. nigra) is a tall, slender tree with ascending branches forming a rounded crown.
Look at the "fruits." The blackjack oak has light-brown, oblong acorns that are about ¾-inches long, while the Chapman oak produces acorns with warty, knobby cups that cover nearly half the fruit. The post oak has ¾-inch acorns with slight stripes and cups covering about one-third of the nut, which are attached to stout, fuzzy brown twigs. The Southern red oak's acorns are ½-inch long and are orange-brown.
Study the bark. The black oak (Q. velutina) has reddish-brown twigs and dark-brown, smooth bark on its trunk with orange-red inner bark that becomes thick and scaly with deep, vertical furrows. The Shumard oak (Q. shumardii) has thick bark with whitish, scaly ridges and deep, darker fissures. The turkey oak (Q. laevis) has scaly, dark-gray bark, turning almost black, with red inner bark and irregular fissures.
Identify the tree by where it's growing. The blackjack, bluejack, post, turkey and Southern red (Q. falcata) oaks grow in dry, sandy, infertile and upland soils or slopes. The swamp chestnut (Q. michauxii), willow, water, overcup, Shumard and swamp red oak trees grow in bottomlands, or near swamps or streams, in moist, poorly-draining soils. The myrtle oak grows near salt water, while the live oak grows in sandy soils in the Florida plains.