Valley Oak

California White Oak, Roble
Quercus lobata
NATIVE – CA ENDEMIC

Description (Jepson, PlantID.net)

• Eudicotyledon
  • Eudicots are a major lineage of flowering plants; see family for general characteristics
• Oak Family (Fagaceae)
• Large winter-deciduous tree, with a broad canopy and contorted branches
  • Largest California oak and may be the largest North American oak: trunk may be 6-7 ft. in diameter and reach more than 100 ft. (Pavlik 2014)
• Thick, ridged bark resembles alligator hide
• Leaves
  • Oblong to ovate with deep lobes
  • Upper surface dark green
  • Underside pale green, covered in soft fuzz
• Flowers
  • Separate male and female flowers on same plant (monoecious)
  • Male flowers on yellow-green catkins (long hanging clusters of small, petalless, unisexual flowers)
  • Female flowers are inconspicuous and often solitary, growing at leaf junctions of new branches
    • Ovary inferior (below the attachment of other flower parts)
• Wind pollinated – see Oak family to learn more
• Fruit is a long, slender acorn held in a warty, knobbed acorn cup; matures in 1 year
• Lifespan may reach 400-500+ years

Distribution

• Native and endemic (limited) to California
  • Grows generally in areas with rich, deep alluvial soils, in valley woodlands, low-elevation riparian forests, and savannas
  • See Calflora for statewide observations of this plant
• Most abundant at elevations to 2,000 ft. but can be found up to 5,600 ft.

Uses (San Mateo County Parks prohibits removal of any natural material)

• Wildlife
  • Oaks are a keystone species, supporting a great number and variety of wildlife and other plants
  • Provide food (acorns, leaves, roots) and habitat for many mammals, birds, butterflies, amphibians, and insects
  • Large mature trees, dead trees, and those with broken limbs are especially important for cavity-seeking mammals and birds
  • Pollen source for bees
    • Bees do not help pollinate oaks, which are wind-pollinated, because female oak flowers offer no nectar, so there is no incentive for the bee to visit and thus transfer pollen
  • Oaks, particularly those in the white oak lineage, host more gall insects than any other native tree or shrub in the western United States (Pavlik 2014 and Russo 2006)
    • Galls are abnormal, tumorlike growths induced by parasites (e.g. insects, mites, or bacteria)
    • Many species of gall (cynipid) wasps co-opt an oak’s DNA to create a unique home and food for their larvae
    • “Oak apple” galls, commonly found on valley oaks, may exceed 3 in. in diameter and are the largest insect galls in the western states
    • Watch this short video on the amazing worlds of oak galls (KQED 2014)
  • Provide a substrate for lichens, mosses, and parasitic plants, like mistletoe
• Native people
  • Oak acorns were an important food for Native people, who gathered them each fall, leached out the tannins, and ground them for making mush or bread
  • Logs used as building material
  • Bark used to blacken strands of red buds for basket making
  • Bark used medicinally
    • Decoction of bark taken as a cough medicine
    • Pulverized outer bark dusted on running sores and particularly used for babies with sore umbilicus
• Other Human Uses
  • Commercial value limited
  • Used for firewood and charcoal production
  • Structures in the wood cells make wood impermeable to water, making it good for watertight barrels

Name Derivation

• Quercus (KWER-kus) – from the Latin for “oaks” from classical times, of uncertain origin; possibly from the Celtic, quer, “fine,” and cuez, “tree”
• lobata (lo-BAY-ta) – from the Medieval Latin lobus, “lobe,” referring to the lobed leaves
• Valley oak – found on fertile bottomland soils

Adaptations

• Produces an especially abundant acorn crop (a mast) in highly irregular cycles; see Oak family to learn more

Notes

• In the white oak evolutionary lineage (Section Quercus), commonly called the white oak group; see Oak family to learn more about these lineages
• Each catkin has 25 to 100 individual male flowers, and each tree bears thousands of catkins in any given year (Pavlik 2014)
• Called the “monarch of California’s oaks” for its great size, age, and beauty (Pavlik 2014)
• Nearby “White Oaks” neighborhood in San Carlos is named for its once numerous old valley oaks
• In decline due to loss of lowland habitat and lowering of water table

ID Tips

• See Oak family for comparative chart of oak lineages
• May be confused with blue oak (Q. douglasii)
  • Valley oaks have deeply-lobed leaves
  • Blue oak leaves have a bluish-green color and much shallower lobing (sometimes just wavy-edged)

At Edgewood

• Found in open grasslands, mixed woodlands
  • See iNaturalist for observations of this plant
• Flowers March – May

See General References

Specific References

Howard, J.L. 1992. Quercus lobata. Fire Effects Information System. United States Department of Agriculture, Forest Service, Rocky Mountain Research Station, Fire Sciences Laboratory.

KQED San Francisco. 2014, Nov. 18. What gall! The crazy cribs of parasitic wasps [Video]. Deep Look. YouTube.

Pavlik, B., et al. 2014. Oaks of California. Cachuma Press, Los Olivos, California, and the California Oak Foundation.

U.S. Forest Service. Wind and water pollination. Forest Service. United States Department of Agriculture.

Wilken, D. and J. Burgher. 2003. California White Oak Quercus lobata Nee. Plant Guide. United States Department of Agriculture, Natural Resources Conservation Service, National Plant Data Center c/o Santa Barbara Botanic Garden, Santa Barbara, California.