Coast Live Oak

Coast Live Oak © DSchiel

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)
  • Evergreen tree
  • 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
Male Flowers (L), Female Flower (M), Acorns (R)
© DSchiel (L,R), SBernhard (M)

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
    • 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
  • 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
Young Tree with Protective Collar © SBernhard

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
Pumpkin Gall © DSchiel

Notes

  • In the red oak evolutionary lineage (Section Lobatae), commonly called the red oak group; see Oak family to learn more about these lineages
  • Catkins have 25 to 100 individual 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)
  • Oaks host more gall insects than any other native tree or shrub in the western United States (Pavlik 2014)
    • 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
  • Edgewood’s coast live oak is classified as a variety
    • Subspecies rank is used to recognize geographic distinctiveness, whereas variety rank is appropriate for variants seen throughout the geographic range of the species; in practice, these two ranks are not distinct
  • 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
Underside of Leaf of Coast Live Oak (L), Leather Oak (LM), Holly-leaved Cherry (RM), Coast Silk Tassel (R) © DSchiel
Coast Live OakLeather OakHolly-leaved CherryCoast Silk Tassel
Leaves
   Shapeovateoblong to ellipticwidely ovate to roundelliptic
   Marginoften wavy and curled

some spines
wavy and curled

many spines
wavy, but not curled

many spines
often wavy and curled

no spines
   Upper Surfacematte 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 Surfacelighter green

possible hairy tufts at vein junctions
matte green

densely hairy
very shiny bright green

no hairs
gray-green

densely matted hairs
Flowersmale 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
Fruitsacornsacornsdrupesclustered 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.

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.