This profusion of common names partly reflects an ongoing controversy about the classification of various live oaks, in particular its near relatives among the white oaks (Quercus subgenus Quercus, section Quercus). Some authors recognize as distinct species forms that others consider to be varieties of Quercus virginiana. Notably, the following two taxa, treated as species in the Flora of North America, are treated as varieties of Southern live oak by the United States Forest Service:
Matters are further complicated by the fact that Southern live oak hybridizes with both the above two species, and also with dwarf live oak (Q. minima), swamp white oak (Q. bicolor), Durand oak (Q. durandi), overcup oak (Q. lyrata), bur oak (Q. macrocarpa), and post oak (Q. stellata).
Typical Southern live oaks are found from southeast Virginia to Florida, including the Florida Keys, and west to southeast Texas. Texas live oaks grow primarily in Texas, on the Edwards Plateau and the Rio Grande Plain, but can be found as far west as Terrell County, Texas, in southwestern Oklahoma and northeastern Mexico. Sand live oaks grow from North Carolina to Florida in the east and Mississippi in the west.
Depending on the growing conditions, live oaks vary from the shrubby to large and spreading: typical open-grown trees reach 15 metres (50 feet) in height, but may span nearly 50 metres. Their lower limbs often sweep down towards the ground before curving up again. They can grow at severe angles, and Native Americans used to bend saplings over so that they would grow at extreme angles, to serve as trail markers. They drop their leaves, and grow new ones, within a few weeks in spring. The bark is furrowed longitudinally, and the acorns are small, but long and tapered. Trees frequently have rounded clumps of ball moss or thick drapings of Spanish moss, and mistletoe is often found on them.
Southern live oak can grow in moist to dry sites. They can withstand occasional floods and hurricanes, and are resistant to salt spray and moderate soil salinity. They tend to survive fire, because often a fire will not reach their crowns. Even if a tree is burned, its root crowns and roots usually survive the fire and sprout vigorously. Furthermore live oak forests discourage entry of fire from adjacent communities because they provide dense cover that discourages the growth of a flammable understory. Although they grow best in well-drained sandy soils and loams, they will also grow in clay. Live oaks are also surprisingly hardy. Those of southern provenance can easily be grown in USDA zone 7 and the Oklahoma Live Oak (Quercus virginiana var. fusiformis), having the same evergreen foliage as the Southern variety, can be grown with success in areas as cold as zone 6. Even with significant winter leaf burn, these trees can make a strong comeback during the growing season in more northerly areas such New Jersey, southern Ohio, and southern Connecticut.
Among the animals for which live oak acorns are an important food source are the bobwhite quail, the threatened Florida scrub jay, the wood duck, yellow-bellied sapsucker, wild turkey, black bear, various species of squirrel, and the white-tailed deer. Native Americans extracted an oil from the acorns. The tree crown is very dense, making it valuable for shade, and the species provides nest sites for many other species.
Live oak wood is hard, heavy, and difficult to work, but very strong. In the days of wooden ships, live oaks were the preferred source of the framework timbers of the ship, using the natural trunk and branch angles for their strength. The USS Constitution was constructed from Southern live oak wood harvested from St. Simons Island, Georgia, and the density of the wood grain allowed it to survive cannonade; even today the U.S. Navy owns extensive live oak tracts. Southern live oak is long-lived. Trees in excess of 500 years were once common, and one, the Angel Oak on Johns Island, South Carolina is estimated at 1400 years of age; it is 20 m tall, 2.47 m diameter, and with a maximum spread (longest branch) of 27 m; the crown covers an area of 1,580 m2. It is threatened by nearby development.
A few cities have managed to preserve their trees, and live oaks, often draped with Spanish moss, are part of the charm of southern cities like New Orleans, Baton Rouge, Mobile, Charleston, Hilton Head Island, Beaufort, South Carolina, Georgetown, South Carolina, Ocala, Florida, Tallahassee, St. Simons Island, Georgia, Brunswick, Georgia, and Savannah, Georgia where they are used as street trees.
See also: Treaty Oak