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Bundle scars, Abby Jones, 2009

Male Catkin, Abby Jones, 2009

Compound leaf, Abby Jones, 2009

Bark Pattern, Abby Jones, 2009

Juglans californica Southern California Black Walnut

Older Specimen, Abby Jones, 2009

Fruit, Abby Jones, 2009 Younger Specimen, Abby Jones, 2009

Opened fruit, Abby Jones, 2009

TAXONOMY Family: Juglandacaea Species: Juglans californica, Two varieties: J.c. var. californica (Southern California Black Walnut) and J. c. var. hindsii (Northern California Black Walnut) Common Name: Southern California Black Walnut Identification Key: 1. Leaflets oblong to elliptic, 7–9 J. regia 1’ Leaflets lanceolate to ovate, 11–19 J. californica 2. Fruit (including husk) generally 2–3 cm diam var. californica 2’ Fruit (including husk) generally 3–3.5 cm diam var. hindsii

GENERAL BOTANICAL CHARACTERISTICS Trees in savanna woodland tend to have multiple trunks. Trees in dense stands tend to be single-stemmed and taller. The trunk is scented and blackish brown. It becomes deeply furrowed with age. The root system is extensive, often with a deep taproot. Trees live to about 100 years. Form: Tree or shrub, 15-50ft. tall and wide, irregular shape Flowers: Southern California walnut is monoecious (male and female flowers on same plant.) Male catkins develop on the wood of the previous year. Female flowers occur singly or in clusters in short terminal spikes. Flowering begins in late winter. Flowers are indistinct. Fruits: Develop during spring, and mature by late summer. The fruit is contained in a husk that does not open at maturity, 2-3cm in diameter. Walnuts produce fruits at 5 to 8 years of age. In drought years little or no fruit is produced. Seeds germinate within 4 weeks of dispersal. Seeds are killed by fire. Fruits are edible. Leaves: Pinnately compound, 6-12in long, medium to dark green, 11-19 leaflets each 2-6cm long, winter deciduous

George B. Sudworth. 1907

GROWING CONDITIONS Occur mostly on north slopes, creekbeds, canyon bottoms, and alluvial terraces. Trees grow best in deep, alluvial soils with high water-holding capacity. Tolerates seasonal flooding. pH: 6.00 to 8.00 USDA zones: 8 to 10 Sunset zones: 18-24 Rainfall: 77cm. to 175cm. Elevation: 500 to 2,500 feet elevation typical, up to 3500ft. possible Soil: High clay content Sun: Partial shade WUCOLS: Low

MANAGEMENT CONSIDERATIONS Walnuts are an allelopathic plant making them difficult to garden under. Uses: Wildlife habitat (deer, nesting birds, rodents, raptors, and California ground squirrels,) food for rodents, fruits edible, Native Americans used shells for dice, bark for baskets, and nuts for dye Landscape Uses: Background, parks, erosion control, wildlife gardens, edible gardens, medium texture, shade tree, slopes

Human Threats: Communities are in decline. Threats include urban and rural development, overgrazing, and increased recreational use of walnut woodlands. Pathogens: Crown rots (Phytophthora spp.) and heart rot.

DISTRIBUTION Endemic to California. Most prevalent along Santa Clarita River, Simi Hills, Santa Susana Mountains, the north slope of the Santa Monica Mountains, San Jose Hills, Puente, and Chino hills. The best remaining stands are in the San Jose Hills. It also occurs in Santa Barbara, western San Bernardino, and northern San Diego counties. Additionally, this walnut is cultivated in Hawaii. Plant communities: Southern Oak Woodlands, Chaparral, Coastal Sagebrush Plant Associations: Coast live oak (Quercus agrifolia) frequently codominants in the walnut woodland. Other associated species include arroyo willow (Salix lasiolepis), California sycamore (Platanus racemosa), white alder (Alnus rhombifolia), California bay (Umbellularia californica), laurel sumac (Malosma laurina), sugar sumac (Rhus ovata), toyon (Heteromeles arbutifolia), Mexican elder (Sambucus mexicana), redberry (Rhamnus crocea), coffeeberry (R. californica), hollyleaf cherry (Prunus ilicifolia), birchleaf mountain-mahogany (Cercocarpus California&statefips=06&symbol=JUCA betuloides), California scrub oak (Quercus dumosa), poison-oak (Toxicodendron diversilobum), spiny ceanothus (Ceanothus spinosus), bigpod ceanothus (C. megacarpus), California sagebrush (Artemisia californica), California buckwheat (Eriogonum fasciculatum), black sage (Salvia mellifera), fuschiaflower gooseberry (Ribes speciosum), brome (Bromus spp.), wild oat (Avena fatua), sweetscented bedstraw (Galium triflorum), rape mustard (Brassica rapa), wildrye (Elymus spp.), and Mexican whorled milkweed (Asclepias fascicularis.)

FIRE ADAPTATIONS Sprouts from the root crown and trunk following cutting or burning. Trees have large woody platforms at the soil surface which shields meristem tissue from fire. After fire, sprouts surround the platforms result in multiple trunks. Trees root crown or root sucker. Most seeds are killed by fire.

SOURCES Charlotte Clarke. 1977. Edible and Useful Plants of California. University of California Press, Berkeley. p94-5 Kathleen Brenzel (ed.) 2007. Sunset Western Garden Book. Sunset Publishing. 8th edition. 417-418, Esser, Lora. 1993. Juglans californica. In: Fire Effects Information System U.S. Department of Agriculture, Forest Service, George B. Sudworth. 1907. “Forest Trees of the Pacific Slope.� USDA,

Abby Jones, LA540 Plant Ecology and Design, Dept. of Landscape Architecture, Cal Poly Pomona

Southern California Black Walnut - ID and facts  
Southern California Black Walnut - ID and facts  

This document includes information about Southern California Black Walnuts and how to identify them in the field.