Juglans californica, the California black walnut, also called the California walnut, or the Southern California black walnut,[1] is a large shrub or small tree (about 20–49 feet (6.1–14.9 m)[3]) of the walnut family, Juglandaceae, endemic to the Central Valley and the Coast Range valleys from Northern to Southern California.
Juglans californica can be either a large shrub with 1–5 trunks, or a small, single-trunked tree. The main trunk can fork close to the ground, making it look like two trees that have grown together, then diverged. It has thick bark, deeply channeled or furrowed at maturity. It has large, pinnately compound leaves with 11–19 lanceolate leaflets with toothed margins and no hair in the vein angles.[4] It has a small hard nut in a shallowly grooved, thick shell that is difficult to remove.
Juglans californica is cultivated throughout California to support the walnut industry, used as a rootstock in English walnut orchards. It is also cultivated as an ornamental tree where it is planted in California native plant, xeriscape, and wildlife habitat gardens and natural landscaping in California, and in Hawaii.
Some authorities (e.g. the California Native Plant Society) combine this species with Juglans hindsii. On the other hand, a 2007 molecular analysis of the genus[6] suggests J. californica is sister to the remaining black walnuts (section Rhysocaryon). This article follows the conventions of The Jepson Manual.[7][8]
^Aradhya, M. K, D. Potter, F. Gao, & C. J. Simon: "Molecular phylogeny of Juglans (Juglandaceae): a biogeographic perspective: Tree Genetics & Genomes (2007)3:363–378
Anderson, E. N. "Some preliminary observations on the California black walnut (Juglans californica)" in Fremontia: A Journal of the California Native Plant Society. January 2002.
