California White Oak, Roble
NATIVE – CA ENDEMIC
- Eudicots are a major lineage of flowering plants; see family for general characteristics
- Oak Family (Fagaceae)
- Thick, ridged bark resembling alligator hide
- Oblong to ovate with deep lobes
- Upper surface dark green
- Underside pale green, covered in soft fuzz
- 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
- Largest North American oak: trunk may be 6-7 ft. in diameter and reach more than 100 ft.
- May live to 400-500+ years
- 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)
- 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
- Provide a substrate for lichens, mosses, and parasitic plants, like mistletoe
- Native people had many uses for valley oaks
- 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
- Limited value as a lumber product; used for firewood and charcoal production
- Structures in wood cells make wood impermeable to water, so good for watertight barrels
- 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
- Produces an especially abundant acorn crop (a mast) in irregular cycles, about every 5 years; see Oak family to learn more
- 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 flowers, and each tree bears thousands of catkins in any given year (Pavlik 2014)
- Called the “‘monarch of the 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
- 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)
- Many species of insects can co-opt the oak’s DNA to create a unique home and food for their larvae in the form of a gall
- An insect-induced gall, called an “oak apple,” is commonly found on the valley oak and is the largest insect gall in the western states; this initially green, ball-shaped gall, created by a cynipid wasp, turns beige by fall and can be more than 3 in. in diameter
- See Oak family for comparative chart of oak lineages
- May be confused with blue oaks (Q. douglasii)
- Valley oaks have deeply-lobed leaves
- Blue oak leaves have a bluish-green color and much shallower lobing (sometimes just wavy-edged)
- Found in open grasslands, mixed woodlands
- See iNaturalist for observations of this plant
- Flowers March – May
Howard, J.L. 1992. Quercus lobata. Fire Effects Information System. U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station, Fire Sciences Laboratory.
Pavlik, B., et al. 2014. Oaks of California.
Cachuma Press, Los Olivos, California, and the California Oak Foundation.
US Forest Service. Celebrating Flowers: Wind and Water Pollination. United States Department of Agriculture.
Wilken, D. and Burgher, J. 2003. Plant Guide: California White Oak (Quercus lobata Nee). U.S. Department of Agriculture, Natural Resources Conservation Service, National Plant Data Center. Santa Barbara Botanic Garden, Santa Barbara, California.