The tree is usually <30' tall, and often has multiple trunks. © Joan Avise

California Black Walnut

Juglans californica

Common on hillsides in oak woodland and grassland with scattered trees in Chino Hills, Santa Ana Canyon and Santa Ana Mtns.  There are trees that were planted in 1974 along SR74 which are now propagating into adjacent wilderness areas.   

Walnuts are monoecious, bearing separate male and female flowers on the same tree. Petals and sepals are lacking from both types of flower. Catkins (male inflorescences) are produced laterally on one-year old wood, and female flowers are produced terminally in spikes of 2-6 on current season’s wood. Walnuts are self-fertile and wind-pollinated, but self-fertilization is prevented because male flowers shed pollen before the female flowers on the same tree can receive it.

Although many trees and small populations have established themselves through Orange County, probably the only naturally occuring populations are those in the Northern portions of the county. Others trees, such as along Santiago Canyon Road, Laguna Canyon Road, Silverado Canyon Road and elsewhere are probably all from cultivation.

Thousand Cankers Black Walnut Disease, a fatal black fungus identified in 2008, is killing many of these trees in both eastern and western US.  It is introduced just under the tree's bark by the Walnut Twig Beetle (Pityophthorous juglandis).

Back to Juglandaceae of Orange County, California
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Silverado Trk. Trail, Western Silv. Cyn., 11-13-11. © Ron Vanderhoff

Irvine Mesa, Silverado Trk. Trail, Western Silv. Cyn., 11-13-11. © Ron Vanderhoff

Williams Cyn., Santa Ana Mts., 5-12-12. © Ron Vanderhoff

South end of Stagecoach Trail, Laurel Canyon, Laguna Coast Wilderness Park, Laguna Beach, Orange County, CA. © Peter J. Bryant

Thick furrowed bark 8-11-07. © Joan Avise

South end of Stagecoach Trail, Laurel Canyon, Laguna Coast Wilderness Park, Laguna Beach, Orange County, CA. 4-7-13. © Ron Vanderhoff

The 8" pinnately compound leaves have 11-15 leaflets. 7-20-11. © Joan Avise

Leaflets. © Joan Avise

Deciduous compound leaves with 11-19 leaflets 7-20-11. © Joan Avise

Hwy 74, 2.5 miles E of Hot Springs Rd., 8-23-12. © Ron Vanderhoff
 

Catkins (male inflorescences) produced laterally on one-year old wood. South end of Stagecoach Trail, Laurel Canyon, Laguna Coast Wilderness Park, Laguna Beach, Orange County, CA. 4-7-13. © Ron Vanderhoff


Catkins (male inflorescences). South end of Stagecoach Trail, Laurel Canyon, Laguna Coast Wilderness Park, Laguna Beach, Orange County, CA. 4-7-13. © Ron Vanderhoff


Catkins (male inflorescences) produced laterally on one-year old wood. South end of Stagecoach Trail, Laurel Canyon, Laguna Coast Wilderness Park, Laguna Beach, Orange County, CA. © Peter J. Bryant


Catkins (male inflorescences) produced laterally on one-year old wood. South end of Stagecoach Trail, Laurel Canyon, Laguna Coast Wilderness Park, Laguna Beach, Orange County, CA. 4-7-13. © Ron Vanderhoff

Catkins (male inflorescences). South end of Stagecoach Trail, Laurel Canyon, Laguna Coast Wilderness Park, Laguna Beach, Orange County, CA. © Peter J. Bryant

Catkins (male inflorescences). South end of Stagecoach Trail, Laurel Canyon, Laguna Coast Wilderness Park, Laguna Beach, Orange County, CA. © Peter J. Bryant

Female flowers are produced terminally in spikes of 2-6 on current season’s wood. South end of Stagecoach Trail, Laurel Canyon, Laguna Coast Wilderness Park, Laguna Beach, Orange County, CA. © Peter J. Bryant

Female flowers are produced terminally in spikes of 2-6 on current season’s wood. South end of Stagecoach Trail, Laurel Canyon, Laguna Coast Wilderness Park, Laguna Beach, Orange County, CA. © Peter J. Bryant

Female flowers are produced terminally in spikes of 2-6 on current season’s wood. South end of Stagecoach Trail, Laurel Canyon, Laguna Coast Wilderness Park, Laguna Beach, Orange County, CA. © Peter J. Bryant
 

Fruit. Hwy 74, 2.5 miles E of Hot Springs Rd., 8-23-12. © Ron Vanderhoff

Fruit. Hwy 74, 2.5 miles E of Hot Springs Rd., 8-23-12. © Ron Vanderhoff


Fruits can grow to 1 1/4 inch and nuts 1". Green fruit on tree, 8-11-07. © Joan Avise


Green husk on fallen fruit 7-20-11. © Joan Avise

Same fruit aged three months 10-7-11. © Joan Avise

Cross section of thick-shelled nut 10-7-11. © Joan Avise

Fall colors. Aliso Creek, vic. Awma Rd., Laguna Niguel;, 11-16-15. © Ron Vanderhoff

Fall colors. Aliso Creek, vic. Awma Rd., Laguna Niguel;, 11-16-15. © Ron Vanderhoff