Quarter Sliced White Oak

My goodness, this could be a tough one. In its publication number FS-247, the United States Department of Agriculture Forest Service lists no less than 11 completely different species of oak that collectively make up the commercial designation "red oak." These species are differentiated from the 10 completely different species of oak that collectively make up the commercial designation "white oak." This does not include the approximately 40 more species of oak that are not commonly harvested, but that grow throughout the lower 48 states of the US and the southern provinces of Canada. All of these are from the genus "Quercus." The designation "spp." indicates there are numerous species within the genus, and I will mention some of these below.

The two botanical groups or sub-genera into which all oaks fall are Leucobalanus for the white oaks and Erythrobalanus for the red oaks.  

Northern Red Oak Tree (Quercus rubra)

Typically, the macro features that

distinguish the two groups are the leaf configuration (white oaks have rounded lobes; red oaks have pointed lobes), acorn taste and development (white oak produces sweeter acorns in one growing season; red oak acorns are more bitter, and require two growing seasons to mature), the bark (white oak is often lighter and scaly; red oak is darker and usually furrowed), and the appearance of the wood rays on the surface of the sawn wood (red oak typically has narrow, short rays; white oak normally has wider, somewhat longer rays). White oak is typically not considered porous due to the inclusion of a substance known as tyloses that impacts its pores, giving it that water tight attribute that makes it desirable for tight cooperage (whiskey barrels).  Red oak pores are generally open to the extent that you can dip one end of a short specimen of red oak into soapy water, and blow through the other end to produce bubbles. Both species grow under similar conditions, and it is not unusual to find both in the same stands of timber.

There is an actual species red oak. In fact there are two: Southern red oak (Quercus falcata) and Northern red oak (Quercus rubra). They are both in the red oak class along with numerous other oaks that include scarlet oak (Q. coccinea), water oak (Q. nigra), pin oak (Q. palustris), shumard oak (Q. shumardii), and black oak (Q. velutina), among others.

There are actually three species with the name "white oak." These include white oak (Quercus alba), swamp white oak (Q. bicolor), and Oregon white oak (Q. garryana). Other oaks in the white oak sub-genera include overcup oak (Q. lyrata), swamp chestnut oak (Q. michauxii), chinkapin oak (Q. muehlenbergii), post oak (Q. stellata), and live oak (Q. virginiana). 

Rotary Peeled Red Oak

 

For technical specifications, we could be talking about a number of values, but let's try this to start. Red oak ranges in dry modulus of rupture (MOR-relative breaking strength) from 10,400 psi for pin oak to 18,100 psi for cherrybark oak (Q. pagodifolia, or Q. falcata var.). White oak moduli of rupture range from 10,300 psi for burr oak (Q. macrocarpa) to 18,400 psi for live oak. Dry red oak moduli of elasticity (MOE-relative bending strength) ranges from 1.49 million psi for southern red oak to 2.28 million psi for cherrybark oak. The numbers for white oak range from 1.03 million psi for burr oak to 1.98 million psi for live oak. Hardness (the pressure required to cause a .444" steel ball to penetrate into the wood surface 1/2 of its diameter) ranges from 1060 pounds for dry red oak to 1480 pounds for dry cherrybark oak. In white oaks, the numbers are 1130 pounds for dry chestnut oak (Q. prinus) to 1620 pounds for dry swamp white oak. Red oak specific gravity ranges from .59 for dry southern red oak to .69 for dry willow oak (Q. phellos). White oak specific gravities range from .63 for dry overcup oak to .88 for dry live oak.   

Rift Cut Red Oak

When you compare the numbers, you see that all the various species of oaks are relatively strong, and reasonably close in physical properties. They all machine relatively well, and take finishing materials nicely. They are highly desired for both their physical strength for structural applications, as well as their aesthetic beauty. Once harvested, all the species are lumped into one of the two groups, depending on the characteristics listed above. For all intents and purposes, they then become indistinguishable from each other to all but the eye of the wood scientist, and then only with the use of high powered magnification."

Final Note:

Occasionally, we hear the name "oak" applied to species that are not of the Quercus genus.  Just remember, whether it's Brazilian Oak, Australian Silky Oak, or Tasmanian Oak (none of which are true oaks), if the genus isn't Quercus, it isn't really oak!