Coast Live Oak

Encina
Quercus agrifolia var. agrifolia
NATIVE

Description (Jepson, PlantID.net)

• Eudicotyledon
  • Eudicots are a major lineage of flowering plants; see family for general characteristics
• Oak Family (Fagaceae)
• Large evergreen tree with a dense, rounded crown
• Bark of young trees is silvery gray and smooth, developing deep furrows and ridges with age
• Leaves
  • Margins spine-tipped and often curled
  • Leaf shape and size varies, often on the same tree
• Flowers
  • Separate male and female flowers on the same plant (monoecious)
  • Male flowers on yellow-green catkins (long hanging clusters of small, petalless, unisexual flowers)
  • Female flowers 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 an acorn, which matures in 1 year
  • Acorns of other red oak species mature in 2 years
• Height to 40 ft. with a diameter of 1 to 4 ft. and crowns to 130 ft. across
• Average lifespan of 300 years

Distribution

• Native to California
  • Grows in mixed-evergreen forest, oak woodlands, chaparral, coastal sagebrush, and valley grasslands
    • Only California native oak that thrives in the coastal environment; normally grows within 60 mi. of the Pacific Ocean
  • See Calflora for statewide observations of this plant
• Outside California, grows into northern Baja California, Mexico
• Grows at elevations to 4,700 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
  • Especially important for cavity-seeking mammals and birds for food-storage, nesting, and protection
  • Larval food source (host) for moths and butterflies, e.g. California sister (Adelpha bredowii californica) and California hairstreak (Satyrium californicum) butterflies
    • In some years, California oak moth larvae (Phryganidia californica) can defoliated entire woodlands (Swain 2009)
    • Healthy trees can survive extensive leaf loss
  • 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 host more gall insects than any other native tree or shrub in the western United States (Pavlik 2014)
    • 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
    • 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 the tannins, and ground them for making mush or bread
• Other Human Uses
  • Wood made a high-quality charcoal used for lime kilns and by blacksmiths where intense heat was required
  • Coast live oak has little commercial value except as a fuel because trunks are rarely straight and the wood warps on drying

Name Derivation

• Quercus (KWER-kus) – from the Latin for “oaks” from classical times; possibly from the Celtic quer,“fine,” and cuez, “tree”
• agrifolia (ag-ri-FO-lee-a) – from the Latin agri,“field,” and folium, “leaf,” but many authorities believe the describing botanist or the printer made an error and that the name should have been aquifolia, “holly-leaved”…. (Charter 2015)
• Coast live oak – “coast” as it is the only California oak adapted to thrive along the coasts; “live” refers to it being evergreen

Adaptations

• Tough evergreen leaves protect against water loss and allow a quick response to favorable conditions for year-long photosynthesis
  • Trade off – evergreen leaves are metabolically costly to build and maintain
• Leaves often vary even on the same tree as the tree adapts to varying degrees of light
  • Outer canopy leaves tend to be smaller and thicker, with extra layers of photosynthetic cells to capture sunlight
  • Inner, shaded canopy leaves tend to be thinner, wider, and flatter, with only one layer of photosynthetic cells to capture the remaining filtered light
• Have you noticed young coast live oaks that appear to have a collar at their base?
  • Young tree will respond to deer browsing by growing as a low, dense bush with small, very spiny leaves
  • When the tree is wide enough that deer can no longer reach the center, the trunk will shoot up and leaves will get larger and less spiny (Heiple 2020)
• Produces an especially abundant acorn crop (a mast) in highly irregular cycles; see Oak family to learn more
• Acorn dispersal is adapted to maximize reproductive success (Steinberg 2002)
  • Most acorns drop in the fall, but, unlike those of other California oaks, some remain attached until spring, reducing loss to birds and small mammals

Notes

• In the red oak evolutionary lineage (Section Lobatae), commonly called the red oak group; see Oak family to learn more about these lineages
  • Some coast live oaks on Edgewood’s northside are hybrids with black oaks (Quercus kelloggii), which are also in the red oak group (Heiple 2023)
    • Black oaks, found in the Santa Cruz Mountains and in the mid-altitudes of the Sierra Nevada, are adapted to cooler habitats
    • Edgewood’s north side receives cooler coastal weather coming through the Highway 92 gap
    • Look for lobed bristle-tipped leaves and reddish new leaves, characteristics of black oaks
• Catkins have 25 to 100 individual male flowers, and each tree bears thousands of catkins in any given year (Pavlik 2014)
• Seed-caching animals aid in seed dispersal
  • Scrub-jays cache about 5,000 acorns each year, 800 acorns per acre
  • Although 95% of cached acorns will be eaten, the remaining acorns have a higher survival rate than uncached acorns because they’ve been carefully planted!
• Extensive coast live oak woodlands around the Bay Area were cleared for agricultural and urban development
  • Crooked, gnarled growth habit and deep shade of mature coast live oaks created woodlands that seemed enchanted or haunted to early California visitors (Pavlik 2014)
• Edgewood’s coast live oak is classified as a variety
  • Variety indicates a population with small morphological variations, e.g. color, seen throughout the geographic range of the species; interbreeding is possible
  • Subspecies indicates a geographically-separated population with distinct morphological characteristics; when not isolated, interbreeding is possible
  • In practice, botanists have not consistently applied these ranks
• Susceptible to the fungus-like microorganism (Phytophthora ramorum) that causes Sudden Oak Death (SOD)
  • The other species at Edgewood known to be susceptible to SOD is Pacific madrone (Arbutus menziesii) when saplings
  • For a complete list of known hosts and host associates see USDA Risk Analysis for Phytophthora ramorum, pp.6-9

ID Tips

• See Oak family for comparative chart of oak lineages
• Unlike other oaks, coast live oaks have tufts of brown hairs at the vein junctions (armpits) on the leaf undersurface
• May be confused with several evergreen trees/shrubs at Edgewood
  • Leather oak (Q. durata var. durata)
  • Holly-leaved cherry (Prunus ilicifolia ssp. ilicifolia)
  • Coast silk tassel (Garrya elliptica)

	Coast Live Oak	Leather Oak	Holly-leaved Cherry	Coast Silk Tassel
Leaves
Shape	ovate	oblong to elliptic	widely ovate to round	elliptic
Margin	often wavy and curled ⋯ some spines	wavy and curled ⋯ many spines	wavy, but not curled ⋯ many spines	often wavy and curled ⋯ no spines
Upper Surface	matte to shiny dark green ⋯ no hairs	matte to shiny dark green ⋯ hairs when new	very shiny bright green ⋯ no hairs	matte to shiny green ⋯ no hairs
Lower Surface	lighter green ⋯ possible hairy tufts at vein junctions	matte green ⋯ densely hairy	very shiny bright green ⋯ no hairs	gray-green ⋯ densely matted hairs
Flowers	male catkins and small, solitary females ⋯ on same plant	male catkins and small, solitary females ⋯ on same plant	bisexual flowers ⋯ in clusters	male and female catkins ⋯ on separate plants
Fruits	acorns	acorns	drupes	clustered berries

At Edgewood

• Dominant tree in most of Edgewood’s woodlands
  • Many coast live oaks on the north side the preserve show signs of hybridization with black oaks (Quercus kelloggii), having especially large, flat leaves and fuzzy, red new growth (Heiple 2020)
    • Black oaks like a cooler environment and are found nearby in Huddart County Park
    • Coastal air, coming through the 92 gap, cools the northern edge of Edgewood
    • Coast live oaks and black oaks are both in the red oak group (Section Lobatae), so hybridation does occur
  • See iNaturalist for observations of this plant
• Flowers February – April

See General References

Specific References

Beidleman, L.H. and E.N. Kozloff. 2003. Plants of the San Francisco Bay Region: Mendocino to Monterey. University of California, Berkeley.

Heiple, P. 2020, May 22. Personal communication.

Heiple, P. 2023, June 30. Personal communcation.

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.

Steinberg, P.D. 2002. Quercus agrifolia. Fire Effects Information System. United States Department of Agriculture, Forest Service, Rocky Mountain Research Station, Fire Sciences Laboratory.

Swain, S., et. al. 2009, Apr. California oakworm. Statewide Integrated Pest Management Program. University of California Agriculture and Natural Resources (UC ANR).

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