Oak Family

Valley Oak © AFengler

Fagaceae (fag-AY-see-ee)

Iconic Features

  • Shrubs or trees
  • Leaves simple and alternate
  • Male flowers in catkins
  • Fruit an acorn or spiny-burred nut

Description (Jepson)

  • Eudicotyledons (eudicots) – a major lineage of flowering plants including most plants traditionally described as dicots and generally characterized by
    • 2 seed leaves (dicotyledon)
    • Netted (reticulate) leaf venation
    • Flower parts in fours and fives
    • Pollen grains with 3 pores (tricolpate)
    • Vascular bundles in stem arranged in a ring
    • Taproot system
  • Deciduous or evergreen shrubs and trees
  • Leaves
    • Simple (not divided into leaflets); entire (with smooth margins) or lobed
    • Alternate (1 leaf at each junction with stem)
  • Flowers
    • Separate male and female flowers on same plant (monoecious)
    • Male flowers
      • Arranged on softly-colored catkins (long hanging clusters of small, petalless, unisexual flowers)
      • Each catkin has 25 to 100 individual flowers, and each tree bears thousands of catkins in any given year (Pavlik 2014)
    • Female flowers
      • Inconspicuous, growing at leaf junctions of new branches or below catkins
      • Ovary inferior (below the attachment of other flower parts)
  • Fruit is a nut, partly enclosed by a scaly or warty cup (acorn); or 1-3 nuts, enclosed by spiny burs
Cup Scales of Red Oak (L) and White Oak (R) Lineages © DSchiel


  • Oaks are masting species (Koenig 2022; Golden Gate 2012)
    • Most years, oaks produce few or no acorns, instead conserving energy for growth
    • On rare occasions, oaks put tremendous energy into producing an abundant crop, called a masting
      • Mast years occur at highly variable, non-periodic intervals
      • From1980 to 2022, the California Acorn Survey, which surveys 1000 oaks in 25 sites across California, found just 3 mast years (7%), in which the acorn crop was 75% or more above the maximum crop
    • Increased acorn production in mast years ensures that more acorns escape predation, as the predator population cannot consume the amount of available food
    • Masting produces a “trophic cascade,” affecting the number of organisms in the entire local food chain, with ripple effects that last years
      • For example, populations of mammals who feast on acorns increase, thereby hosting more ticks, resulting in a potential increase of Lyme disease
    • Oaks of different species synchronize masting cycles
    • Scientists have not yet determined what triggers a mast year or how species synchronize masting across large areas, but temperature fluctuations may be a cue and thus may be affected by climate change
    • The term mast comes from an Old English word for woodland nuts that gathered on the ground and were used to feed livestock, such as pigs
Oak Leaves © DSchiel


  • Approximately 900 species, generally in the northern hemisphere
    • Includes oaks, chinquapins, beeches, and chestnuts
  • “Oak woodlands are one of the richest broad habitats in the state with well over 300 terrestrial vertebrates utilizing woodlands at some time during the year” (UC ANR 2022)
  • Oaks (Quercus) and beeches (Fagus) are wind pollinated
    • About 12% of flowering plants and most conifers are wind pollinated (U.S. Forest Service)
    • These plants do not waste energy on flower features that attract animal pollinators; instead, their flowers generally have these characteristics
      • Small, petalless, and unscented, with muted colors
      • No nectar
      • Stamen (male flower part) and stigma (pollen-receiving part of the pistil/female structure) are exposed to air currents
      • Male flowers produce a great deal of pollen, which is very small, dry, and easily airborne, as all allergy sufferers know!
  • Chestnuts (Castenea species) and chinquapins (Castanopsis species), unlike oaks, are pollinated by insects (Singh 2019)
    • Flowers produce strong odors to attract pollinators
  • Scientific name from the included genus Fagus, from the Latin for “beech”
  • Represented by 5 native and 1 non-native oak species at Edgewood, as well as many hybrids
    • Coast live oak (Q. agrifolia var. agrifolia) is in the red oak lineage (Section Lobatae), commonly called the red oak group
    • All other native oaks at Edgewood – leather (Q. durata var. durata), valley (Q. lobata), scrub (Q. berberidifolia), and blue (Q. douglasii) – are in the white oak evolutionary lineage (Section Quercus), commonly called the white oak group
    • A single non-native cork oak (Q. suber; Section Serris) grows at the Day Camp picnic area
    • Oaks in the same lineage may hybridize; in fact, in the Bay area, they often do
  • Four of Edgewood’s five native oak species can be found near the junction of the Serpentine and Sylvan trails
    • Valley (Q. lobata), blue (Q. douglasii), and coast live oak (Q. agrifolia var. agrifolia) grow close together trailside on the upper Sylvan trail
    • Look for the young blue oak that grows downhill and to the left of an unusual blue-leather hybrid
    • Leather oak grows trailside on the Serpentine trail near the junction with the Sylvan

Characteristics of the Evolutionary Lineages of Edgewood’s Native Oaks

White Oaks (Section Quercus) Red Oaks (Section Lobatae)
Edgewood Oaks valley, blue, leather, scrub coast live
     Lobes lobed or unlobed lobed or unlobed
     Lobe Shape round pointed
     Margins smooth or with blunt, green teeth or spines tawny bristles and spines
     Inner Shell smooth densely hairy
     Cup Scales thick and knobby thin and flat
     Matures In 1 year 2 years (exception–coast live oak acorns mature in 1 year)
Bark (mature trees) light gray or brown; scaly or rough dark gray, blackish or brown, smooth
Wood light brown or yellowish reddish brown
Adapted from Pavlik, B. et al. 2014. Oaks of California. Cachuma Press, Los Olivos, California, and the California Oak Foundation. Pg. 36.

See General References

Specific References

Golden Gate National Parks Conservancy. 2012, Dec. 29. Critical Mast: The Boom and Bust of Acorns.

Koenig, W.D. 2022, July 5. An enduring oak mystery: Synchronized acorn booms. Bay Nature.

Nixon, K. C. 2002, Summer. The oak (Quercus) biodiversity of California and adjacent regions. R.B. Standiford et al. (Eds.). Proceedings of the Fifth Symposium on Oak Woodlands: Oaks in California’s Challenging Landscape. United States Department of Agriculture, Forest Service, Pacific Southwest Research Station. Pp. 3-20.

Singh, G. 2019. Plant Systematics: An Integrated Approach (4th ed.). CRC Press.

University of California Agriculture and Natural Resources (UC ANR). 2022. Oak woodland wildlife. UC Oaks.

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

Browse Some Edgewood Plants in this Family