Juglans major

Arizona Walnut - Juglans major
New Mexico, USA

First of all, the disclaimer.  There is the possibility that the individual described here is an intergrade between Juglans microcarpa and J. major.  The fruit appear to large to be microcarpa in this case.  At the eastern edge of its range, J. microcarpa intergrades with Juglans nigra.   This is a classic species cline - just where do you draw the line?

The Arizona Walnut (see range map for the United States from BONAP - right) is found as far south as Guerrero in Mexico.  In Mexico the word for walnut is nogal, and you see references to “nogal” on many maps.  Canyons, towns, washes, whatever have been named to indicate the proximity of this species.  Arizona Walnut is the only walnut which is found in the desert.  It is also found at elevations up to 6,500 feet.

The Arizona Walnut is referred to as Arizona Black Walnut in some sources.  Scientific synonyms include; Juglans elaeopyren, J. microcarpa subsp. major, J. microcarpa var. major, and J. rupestris var. major.

There are two varieties of Arizona Walnut which are currently recognized: the nominate form, Juglans major var. major; and J. m. stewartii.  The species was first described by John Torrey.

Arizona Walnut fruit production varies from year to year, with heavier crops every second or third year.  Although arguments have been presented that the crop variation is due to spring precipitation rates, precipitation rates do not match a 2-3 year cycle.  The fruit ripens between July and September, depending on elevation.

The specimen shown below was collected by Dr. Palmer in 1869.

San Lorenzo, NM, USA

© Robert Barnes 2018