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 agrifolia: Coast Live Oak
Quercus agrifolia: Coast Live Oak. An evergreen tree typically 30-75 feet tall with smooth grey bark that develops soft splits as it ages, giving a variable appearance from mostly smooth to almost zebra-striped. Leaves: blade 1-2.25 inches long, oval to round, convex, usually with spines at leaf edge, underside of leaves sometimes with "hairy armpits" at junction of midvein and lateral veins. Number of lateral veins usually limited to 3-5 "pair." Acorns: mature in 1 year (unusual for an oak in this section), with pointed tip, cap usually about as deep as wide, covered with scales and little to no hair.
Quercus kelloggii: Black Oak
Quercus kelloggii: Black Oak. A deciduous tree typically under 75 feet tall with smooth grey young bark that becomes deeply furrowed and dark brown to black as it matures. Leaves: blade 3-7 inches long, deeply lobed with soft bristles adorning the lobe ends. Acorns: mature in 2 years with a rounded tip (ignoring the little spine on the end). The acorn cap is generally as deep as it is wide, often covering most of the acorn shell, with scales and little to no hair.
Quercus parvula: Shreve Oak
Quercus parvula: Shreve Oak. An evergreen tree, typically under 50 feet tall, with smooth grey young bark that eventually furrows to an irregular checkered grey. Leaves: blade 1.5-3.5 inches, mostly flat, oblong to spear tip shaped, generally with a pointy tip that is sometimes slightly askew to one side, leaf edges somewhat variable, often (but not always) without spines. Undersides of leaves are a dull, hairless, light olive-green, generally with >5 "pair" of lateral veins. Petioles 2-25mm, generally hairy on top, almost smooth on bottom. Catkins not clustered, widely spaced. Acorns: mature in 2 years, rounded tip (ignoring the little spine on the end), wooly inside. The acorn cap is bowl shaped, usually wider than it is deep, with thin, flat scales.
Quercus wislizeni: Interior Live Oak
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.
