Juglans hindsii × J. regia Paradox walnut

Paradox Vlach walnuts at Rinconada Park, Palo Alto. Sairus Patel, 12 Oct 2023

A Paradox Vlach walnut fruits at Greer Park, Palo Alto. Sairus Patel, 10 Jul 2023

A hybrid of our native Northern California walnut (J. hindsii) and the common walnut of Eurasia (J. regia), Paradox was developed by master horticulturalist Luther Burbank in the late 1800s. It also arises naturally when pollen from walnut orchards drifts over to our native walnuts nearby. Primarily used as a vigorous rootstock for J. regia, Paradox exhibits intermediate foliage characteristics – typically more leaflets than J. regia, but narrower and edged with minute teeth. (J. regia has smooth margins, though young leaves may show faint serrations.)

Paradox walnut clones of cultivar ‘Vlach’ were used in a 2003 artistic experiment that involved planting paired trees at various sites across San Francisco and the greater Bay Area. More than twenty years later, several Palo Alto locations are thriving: two girthy specimens with immense crowns southeast of the Rinconada Park playground (map pin); one at the southeast corner of Briones Park (map pin); two at the unirrigated dog run in Mitchell Park, near the rear edge of 455 East Charleston Road (map pin); and two at Greer Park, midway between the basketball courts and Amarillo Avenue (map pin). A few of these bore a couple of small walnuts; Paradox is not known to be a heavy fruiter.

It has seemed to do well both in lawn and without irrigation, making it a promising candidate for campus plantings where a large, fruitless deciduous tree is desired. Since some proportion of “native” trees is often desired – or required – in landscaping, would two Paradoxes count as one native walnut or two?