Overview
The Northern California Walnut (Juglans hindsii), also celebrated as Hinds’ Black Walnut, is an imposing, beautiful native hardwood tree endemic to northern California. Named in honor of British botanist Richard Brinsley Hinds who collected it along the Sacramento River in 1837, this rare tree is famous throughout world agriculture as the primary genetic parent of the ‘Paradox’ hybrid rootstock upon which almost all commercial English walnuts are grafted.
Biology and Physical Characteristics
The Northern California Walnut grows into a grand, single-trunked canopy tree reaching up to 25 meters with a magnificent spreading crown. Its dark greyish-brown bark is deeply fissured into rough, diamond ridges. Its alternate pinnately compound leaves are 30 to 45 cm long, bearing 13 to 21 lance-shaped, serrated leaflets that release a rich, aromatic fragrance when bruised. Its spherical nuts are 3 to 5 cm wide, enclosed in a thick, smooth, green husk containing an exceptionally thick, dark shell.
Behavior and Ecology
A dominant riparian canopy tree, its deep, tenacious root system anchors riverbanks against powerful winter floodwaters while accessing subterranean water tables during searing Central Valley summers. Like other walnuts, it produces juglone in its roots and fallen leaves to suppress competing weeds.
Conservation and Human Impact
Listed as Endangered by the IUCN and classified as highly threatened by the California Native Plant Society, only a tiny handful of pure native stands survive in Contra Costa, Napa, and Yolo counties. The species is threatened by extensive agricultural land conversion, river channelization, and extensive hybridization with cultivated English and eastern black walnuts.
Interesting Factoid
Almost every commercial walnut eaten in the United States owes its life to the rare Northern California Walnut: its roots are so tough and immune to soil diseases that farmers graft commercial walnut varieties onto its rootstock.