Jepson (2012) (APG System)





Jepson (1993) (Cronquist System)





Quercus (oak) may be the most important hardwood genus in the world. It forms the basic foundation for hardwood forests throughout North America, Europe and Asia. The tree creates habitat for a wide variety of wildlife and the acorns are a significant food resource. Formerly, people relied heavily on acorn production as well.

Quercus is subdivided into a number of subgroups. The two main groups in California are the White Oaks and the Red Oaks. We placed the Canyon Live Oaks in the red oak group, but they could be shown in the Intermediate Oak group as well.

The White Oaks are characterized by rounded lobes on their leaves, without any bristles on the lobes. A good example is Valley Oak (Quercus lobata). The acorns taste sweet or slightly bitter, and mature in six months. They generally require little or no stratification to germinate.

The Red Oaks (also called the Black Oaks) are characterized by leaves with pointed lobes or no lobes at all. The leaves have bristles. The most significant example is Coast Live Oak (Quercus agrifolia). The acorns taste bitter and require a leaching process to make them edible, and require 18 months to mature. Germination is greatly aided by stratification, although some acorns will germinate without it.

Both types of oaks are found on a wide variety of sites, and the similarities far outweigh the differences. The Red Oak group is the dominant type in California, occuppying a wide variety of niches, from riparian zones to hillside woodlands. Formerly, fire management by the Indians kept red oak woodlands open and parklike. Without fire management, these areas tend to close up and become dense. White Oaks tend more toward valley bottoms, moist soils and open sites.

A major practical distinction is that members of the Red Oak group are susceptible to Sudden Oak Death, while members of the White Group are not.

Quercus (Oak)

California Native Plant Guide
Native Plant Genera

Plant Relationships

California Species:

Red Oaks
Quercus agrifolia

Quercus chrysolepis
Quercus kelloggii
Quercus wislizenii

White Oaks
Quercus douglasii
Quercus dumosa
Quercus durata
Quercus engelmannii
Quercus garryana
Quercus lobata

(Coast live oak)
(Canyon live oak)
(Black oak)
(Interior live oak)

(Blue oak)
(Scrub oak)
(Leather oak)
(Engelman oak)
(Oregon white oak)
(Valley oak)

Other Species:

Quercus alba
Quercus macrocarpa
Quercus palustris

Quercus rubra
Quercus stellata
Quercus suber

(White oak)
(Bur oak)
(Pin oak)
(Red oak)
(Post oak)
(Cork oak)


Growth Forms:

Almost all members of Quercus are trees. Some are described as scrub or brush, but they are essentially just small scrubby trees.




Members of the White Oak group have leaves with rounded lobes and no prickles. The members of the Red Oak group either have leaves with pointed lobes or leaves with no lobes at all. All red oaks have prickles on the tips of the lobes or on the margins of the leaves. Most oaks are deciduous. Some, like the live oaks, are evergreen.


The male catkins emerge in mid to late winter. The female flowers are minute and essentially invisible. I have never seen one.

Oaks are wind pollinated. The difference between a good acorn year and a bad one can depend on the amount of rainfall during flowering season. Too much rain can suppress pollination and the resulting acorn crop.


Oaks produce acorns. The acorns ripen in late summer or early fall. Black oak and Valley oak tend to ripen earlier and live oak tends to ripen later. If you collect acorns, you are in competition with the other wildlife. They will collect the acorns as soon as they fall from the tree. If you are late, dig around in the leaves. You will often find some.


Oak is known for being particularly hard and dense. Oak burns for a long time, and leaves long lasting coals, useful for regenerating a fire after hours of neglect.

Most oaks have straight central leaders and straight trunks, and can be used for furniture and dimensional lumber. Ships, houses, and even cathedral roofs in europe depended on oak beams. East coast oaks tend to have straight trunks. Due to its density, oak is more difficult to shape and work than most other woods. The resulting furniture and cabinets tend to consist of flat pieces with right angle edges. In California, oaks usually have open branching, without a central leader, and have bent and somewhat contorted stems. Only select portions of these trees can be used for furniture. These trees are generally used for firewood.

Oak is vital to the wine industry. Wine is aged in oak barrels. The word "cork" is derived from Quercus. A cork is simply a piece of oak bark.

Growing Conditions

Sun and Exposure:

Oaks are intolerant of shade. They must be in the sun for vigorous, healthy growth. If oaks grow in the shade for too many years, they will not return to vigorous growth, even if shade is removed.

Soil and Moisture Requirements:

Oaks are forest trees, and do best where there is a sufficient moisture supply in the ground, even if they must send down roots to find it. Most oaks are found in typical forest soils and settings, but some handle fairly dry and harsh conditions. Blue oak, for example, is found on dry hills in areas with hot, dry air. It is undoubtedly finding deep moisture, but it is living in a difficult environment.

Natural Habitat and Range:

Oaks are found in temperate forests throughout North America and eurasia. Quercus extends into the semi-tropical rainforests of Central and South America, into the northern Andes.

Horticulture and Restoration

Horticultural Comments:

Oaks are sensitive to changes in their watering regime. If an oak has grown without irrigation, do not add irrigation later, particularly near the base of the tree. If you must irrigate, limit it to the drip line. Do not add soil around the base of the tree. The additional soil will damage and possibly kill the tree.

Oaks are known for being slow growing. This is not particularly true. They will grow as fast as any other tree if they are established and in the right spot. When you install an oak, it can take two or three years for the root system to establish itself. During this time, the top doesn't grow much, and it appears that nothing is going on. Around the third or fourth year, if the tree is happy and properly located, it will start to grow rapidly.

Wildlife Habitat:

Birds nest in the branches. Birds and rodents take up residence in rot holes or where branches have broken off. Acorns are one of the most important food sources in the forest.

Restoration Projects:

Oaks are widely used in restoration projects. They have a high survival rate, but it appears that relatively few really thrive after the installation.

California Native
Plant Guide

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