Palomar College Oaks
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Oaks (Quercus) at Palomar College
Large Genus Of Beautiful Trees Across America
© W.P. Armstrong 10 July 2022
The genus Quercus (Oaks) includes an estimated 600 species worldwide, with 25 species native to California about 20 at Palomar College (as of 10 July 2022). This is an ongoing report on some of the species represented on the Palomar College campus and Arboretum, with links to other species throughout the Wayne's Word website. Oaks are often difficult to identify, especially when hybridization is common between some species. Reproduction of many species is declining due to habitat degradation (urbanization), global warming and disease. Intense, excessive wild fires are also a factor, especially in California, although epicormic coast live oaks (Q. agrifolia) can resprout from dormant buds in branches and fire-resistant trunks under normal wildfire frequencies.

Although I live in a quaint-sounding place called Twin Oaks Valley, the original 2 coast live oaks are long gone. These oaks still try to sprout in my yard and once grew in areas now occupied with housing tracts and golf courses. They have been planted in some of these areas.

  Jepson Key To The Oaks Of California  
Kew Plants Of The World Online  
World Flora Online Home Page
World Flora: Quercus (Oaks)

Oaks in the Edwin & Frances Hunter Arboretum at Palomar College

California Native Oak Species.
A. Engelmann Oak (Quercus engelmannii) San Diego County
B. Scrub Oak (Q. dumosa)--Rare & Endangered San Diego County
C. Coast Live Oak (Q. agrifolia var. agrifolia) San Diego County
D. Valley Oak (Q. lobata) Sacramento Valley
E. Calif. Black Oak (Q. kelloggii) San Diego County
F. Island Oak (Q. tomentella) Catalina Island
G. Blue Oak (Q. douglasii). San Joaquin Valley Spindly oak west side NS Bldg.
H. Scrub Oak (Q. berberidifolia) San Diego County
I. Oak Hybrid. (Q. x acutidens). San Diego Co. Leaves & height resemble this
species; acorns resemble Q. cornelius-mulleri. These spp. & Q. berberidifolia
commonly referred to as scrub oaks, often misidentified as Q. dumosa.

Oaks From Other States & Countries At Palomar College
A. Texas Red Oak (Quercus buckleyi) Texas
B. HollyOak (Quercus ilex) Mediterranean
C. Bur Oak (Q. macrocarpa) Eastern U.S.
D. Encino Amarillo (Q. macrophylla) W. Mexico
E. Japanese Live Oak (Q. myrsinifolia) Asia
F. Pin Oak (Q. palustris) Southeast U.S.
G. Cork Oak (Q. suber) S Europe & NW Africa
H. Southern Live Oak (Q. virginiana) SE U.S.

The following oaks are on my original on-line Wayne's Word arboretum plant list. I have located most of these species as of 7 July 2022:

FAGACEAE: BEECH FAMILY See Riparian Garden: RIP On Map

  1. Quercus agrifolia Coast Live Oak (S. Calif.) M-216 RIP
  2. Q. douglasii Blue Oak (California Foothill Woodland) M-211
  3. Q. x acutidens (not Q. dumosa) Scrub Oak Oaks of San Diego County RIP
  4. Q. engelmannii Engelmann Oak (S. Calif.) M-49 RIP
  5. Q. ilex Holly Oak M-48 RIP (Also many locations on main campus)
  6. Q. lobata Valley Oak (California) M-166
  7. Q. macrocarpa Bur Oak (E. U.S.) M-50 RIP (Also near Board Conference Room)
  8. Q. myrsinifolia Japanese Live Oak (E. Asia) M-145
  9. Q. palustris Pin Oak (Central & Eastern United States) M-215 RIP
  10. Q. phellos Willow Oak (E. U.S.) M-142 (Not located as of 7 July 2022)
  11. Q. shumardii Shumard Red Oak (S.E. U.S.) M-148 (Not located as of 7 July 2022)
  12. Q. virginiana Southern Live Oak (S.E. U.S.) M-147 (Also on main campus)

Additional oaks on list prepared by campus Grounds Supervisor Tony Rangel:

FAGACEAE: BEECH FAMILY See Riparian Garden: RIP On Map

  1. Quercus buckleyi Soccer Field (Texas Red Oak)
  2. Q. cambii (sp?) canbyi Chisos Oak (Texas)
  3. Q. chrysolepis Canyon Live Oak
  4. Q. gravesii Chisos Red Oak
  5. Q. macrophylla syn. magnoliifolia (north of library)
  6. Mossy Cup Oak? syn. Q. macrocarpa
  7. Q. suber Cork Oak (Many places on campus)

During my career I have always been interested in the diversity of oaks (genus Quercus). It may have started as a child back in my home town of Arcadia with my fascination with acorns, the one-seeded fruits of oaks.

The true nut of an acorn sits in a cup-shaped involucre composed of numerous overlapping scales. The 2 acorns in above image are from the cork oak (Quercus suber), the bark of which is the source of natural cork. According to Spjut (1994), the acorn fruit is also called a "glans." For those with an interest in anatomy, glans is the head of a penis. For an in-depth study of fruit types, please refer to the "Systematic Treatment of Fruit Types" by Richard Spjut (Memoirs of New York Botanic Garden, Volume 70, 1994). This scholarly article is based on extensive research of classical fruit nomenclature dating back to the 18th century.

When attempting to key out a California oak species in The Jepson Manual: Vascular Plants of California (2012), you must make an important decision regarding the overlapping acorn cup scales: Are they thin and flat (not tubercled), or are they thick and raised (tubercled). Making the correct choice here will eliminate some of the species to choose from in this couplet dichotomous key.

Some oaks on Palomar Mountain: A. Canyon live oak (Quercus chrysolepis). B. Interior live oak (Q. wislizeni var. frutescens). C. Oracle oak (Q. x morehus), hybrid between "B" and "D."  D. California black oak (Q. kelloggii). All of the acorn cup scales are thin & flat (not tubercled).

I photographed many species of oaks on road trips across the US, dating back to a sabbatical leave in fall, 1976 to the incredibly beautiful deciduous forests of the midwestern & eastern US.

Links To Wayne's Word Pages With Oak Images:

  1. Hybrids2.htm:Oaks of San Diego County
  2. Hybrids1.htm:Hybrid Oaks in San Diego County
  3. The Hybrid Gander Oak (Quercus x ganderi)
  4. Palomar Mountain Oak Acorns
  5. Palomar Arboretum: Q. palustris & Q. macrocarpa
  6. Ariz. White Mtns: Gambel Oak (Q. gambelii)
  7. Chiricahua Mtns: Ariz. White Oak: (Q. arizonica)
  8. Cave Creek Canyon: Ariz. White Oak Gall (Q. arizonica)
  9. Columbia River Gorge, Oregon: Garry Oak (Q. garryana)
  10. E. Arizona: Scrub Oak (Q. turbinella)
  11. Calif. Blue Oaks (Q. douglasii) & Galls
  12. Twin Oaks Valley: Texas Red Oak (Q. buckleyi)

California Oaks Are The Host Of Some Fascinating Galls

Oaks are the host of many fascinating galls occupied by a variety of gall wasps. My favorite are the famous "Jumping Galls" of northern California's Sacramento Valley. They litter the oak-lined streets in some towns and resemble microscopic bouncing ping-pong balls!

  Wayne's Gall Page:To Be Or Not To Be A Gall  
California's Truly Remarkable Jumping Galls!
Mexican Jumping Beans vs. Jumping Galls!

Oaks Provide Food & Habitats For A Variety Of Animals & Native People

Oak trees are important components of complex food webs in forest ecosystems.

Local scrub jays are a major source of seedling coast live oaks at the Wayne's Word headquarters in nearby Twin Oaks Valley. They are usually in places where there is no room for an oak tree.

Bedrock mortars are found throughout San Diego County, especially where native oaks occur. There are also a few in the hills of coastal sage scrub adjacent to Palomar College, including the Palomar College Arboretum. Portable metates have also be found in these hills. There were abundant acorns from coast live oaks in nearby Twin Oaks Valley. Other edible seeds and roots were ground or mashed. Native people were definitely in this area long before the white settlers. The coastal sage scrub and nearby grassy hillsides contained numerous edible bulbs and corms, including brodiaeas (Dichelostemma) and golden stars (Bloomeria). Poisonous native bulb species, such as star lilies (Zigadenus), were avoided.

Acorns Provide The Living Quarters For A Remarkable Ant Species.
Ant nest tunnels can be very crowded but this is an extreme example!

 This little ant is Temnothorax andrei. It was collected in the leaf litter under a coast live oak (Quercus agrifolia). A related species (T. curvispinosus) of the E. U.S. is called the "acorn ant," so named because the queen and entire colony of workers live inside of an acorn! The colony may occupy more than one acorn (polydomy).

Two Good References About California Native & Introduced Oaks

Pavlik, B. M., Muick, P.C., Johnson, S.G., and M. Popper. 1995. Oaks of California.
     Cachuma Press, Inc., Los Olivos, California. 184 p.

Ritter, Matt. 2022. A Californian's Guide To The Trees Among Us. Second Edition.
     Heyday Press, Berkeley, California. 196 p.

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