The Red Oaks (section Lobatae)
Trees in the red oak section are all either evergreen, have bristles or small prickers on their leaves, or both. Acorns of these species all have scaled cups. Black oak has bristles, but is deciduous. Coast, Shreve, and interior live oaks are all evergreen, and leaves can vary highly even on a single tree. These trees can be difficult to tell apart, and all can hybridize with one-another, complicating identification. In general, coast live oak bears acorns in a single year, has broad leaves with few lateral veins (5 or less pair), which often have hairy “armpits” where they join the midvein. Black oak, Shreve oak, and interior live oak all bear acorns in two years. Interior live oak leaves tend to be more oblong than coast live oak, have more lateral veins, and do not have hairs at the latera/midvein junction. Shreve oak is very similar to interior live oak, but has longer petioles (the little stem on which the leaf is carried) which are hairier on the top than on the bottom. Interior live oak petioles are normally uniformly covered with tiny hairs. This normally takes a hand-lens to see.
All oaks in this section are susceptible to sudden oak death to varying degrees.
Quercus wislizeni: Interior Live Oak. An evergreen tree typically 30-65 feet tall, with smooth grey bark that quickly furrows and checkers to darker grey as it matures. Leaves: blade 1-2 inches long, oblong or oval, usually flat, sometimes with a pointy tip, leaf edges often highly variable, showing spines and teeth on some leaves and not on others. Leaf undersides are normally a shiny(ish) yellow green,hairless, and typically exhibit >5 "pair" of lateral veins. Petiole 3-15mm, densely hairy on both upper and lower surfaces. Catkins clustered into groups. Acorns: mature in 2 years, 0.75-1.5in with a slightly pointed end, wooly inside. Acorn cup is bowl shaped, sometimes as deep as it is wide, with thin, flat scales.