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Species Spotlight

Arizona Walnut

By Doug Moore

We are finally emerging from a very cold week- apparently one for the record books - with temperatures that had even hardy winter visitors bundled up and yearning for more tropical climes. The arctic blast got me yearning for spring, definitely warmer temps and real green leaves sprouting profusely upon the deciduous trees in the canyon. Usually, this space is reserved for canyon wildflowers or unusual plants or animals, but feeling somewhat impatient for spring and verdant trees at the moment, I’d like to write about a favorite, but “common” Madera Canyon tree, the Arizona Walnut.

About twenty species of walnuts grow across Eurasia and North America and in the Andes of South America. The Arizona Walnut, Juglans major, is the only native walnut found in Arizona. “Mexican Walnut,” might be a more appropriate name, as its natural range centers in the Sierra Madre Mountains of Mexico. In the U.S., Arizona Walnut grows only in Arizona and New Mexico, with scattered, local remnant populations in west and central Texas. Found primarily along mountain streams from 2,500 to 7,000’, in Madera Canyon, Arizona Walnut is a common component of the riparian forest along the creek and deep tributary drainages from around White House Picnic Area to Josephine Saddle.

Under a rounded crown of widely spreading branches, Arizona Walnut can grow to a height of 50 feet with a grayish-brown, furrowed trunk three feet wide; sometimes trees will have several trunks. Some of the largest walnuts in the canyon, including several of truly impressive stature, grow along the Carrie Nation Trail between the “first pitch” and the Vault Mine Trail intersection. Leaves are up to 14” long and pinnately compound, meaning that each has 9 to 13 coarsely toothed, broadly lance-shaped leaflets. The leaves grow alternately on branches and are aromatic when crushed. Arizona Walnut is deciduous and drops its leaves for winter.

Arizona Walnut blooms in the spring and is wind pollinated. Separate greenish hanging catkins of male flowers and erect clusters of female flowers are produced on the same tree. Round, hard-shelled walnuts develop within a green fleshy husk and mature in the fall. Smaller and rounder than commercial English walnuts, the nutritious nuts are none-the-less quite tasty and relished by squirrels, bears, and other wildlife. People are fond of the walnuts also; the common Spanish name for walnut is nogal. The town of Nogales was named in honor of the Arizona Walnut trees that grew in the area.