Las Pilitas Nursery

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This website is dedicated to Bert Wilson. His genius continues to inspire us.

California Oaks IV

Quercus kelloggii (Kellogg oak or Black oak)and the relationships of California oaks.

Acorn matures in one season (at end of new stems)

Acorn matures in two seasons (on older stems)

I. Evergreen

Quercus agrifolia, Q. x alvordiana, Q.dumosa, Q. durata, Q. sadleriana, Q. turbinella

II. Deciduous

Quercus garryana var. breweri, Q. douglasii, Q.engelmannii, Q. garryana, Q. lobata

III. Evergreen

Quercus chrysolepis, Q. parvula, Q. tomentella, Q. vaccinifolia, Q. wislizenii, Lithocarpus densiflorus (Tanbark Oak)

IV. Deciduous

Q. kelloggii, Q. palmeri

Oak relationship chart

How to take care of your oak trees.


IV. California Oaks that bear acorns on the second season's growth and are deciduous.

Quercus kelloggii leaf - grid24_12

Black Oak, or Quercus kellogii, seems to pick odd spots in most of California to colonize that do not make much sense when first chanced upon.

Leaves of Valley Oak, Quercus lobata - grid24_12
A natural occurring hybrid of Q. lobata and Q. Kellogii that can drive you crazy!
In northern California this Black Oak (Quercus kelloggii) can cover thousands of acres and be the dominant tree in whole forests. In central and southern California the colonies are much more fragmented. The stands usually occur on north slopes(but in Mesa Grande they are a whole forest), usually where the summers are cool (but in Templeton they get into the 100's), usually below snow level (but on Mt. Pinos they may see 10 foot of snow), usually in a wetter spot or where the rainfall exceeds 40 inches, but again, not always. If you are planning to plant this tree in a landscape, look for a cool, north wall that the tree can grow above(maybe 15-20 feet) that stays moist in winter and gradually dries out into fall. Soil types range from granitic, through red clay to alkaline clays.

Below is a relationship map of the California oaks. After wandering around California for 30 years trying to figure out oak species we've come to the conclusion that there are as few as one true species or as many as six. (Quercus lobata, Quercus dumosa, Quercus wislizenii or Q. agrifolia, Quercus kelloggii, and Quercus chrysolepsis.) This causes great difficulties when all the oaks on a hillside are hybrids of the primary oaks. All the other oaks are subspecies, varieties or hybrids of these , AND should be listed as such, not lumped into species, but the stable, reproducing trees should have a name attached, just not a species rank.

The reproductive parts of the plants should be used for species differentiation, but the acorns and catkins are just too diverse, again leading to the conclusion that most of the California oaks are hybrids or variations of only several species. To add to the confusion the chromosome count for all the major oaks is twelve. If they were truly hybrids they would be multiples of twelve. Instead they seem to be varieties or subspecies of one parent oak somewhere back in the past that has reproduced against itself and California's environment for thousands of years to create a redundant swarm of diverse oaks.

It seems to be very much like a color chart. You can determine the oak is green, but is it light green, aqua green, chartreuse, verdant, deep green, tawny green or lime green? There are only five or maybe six that you can walk up to and have no argument about. Most of the others have something else in them, they are not 'clean colors'.

my attempt to trace the relationships of California oaks - grid24_24
Oaks of California