Juglans californica is the most distinctive western walnut, but some care must be taken in identifying it. The distinctive leaflet shape of J . californica is occasionally replicated by early-season leaves of other species. Furthermore, J . californica is distinctive in lacking simple and fasciculate hairs on the leaves, but like most other walnuts, multiradiate hairs are normally present on the young vegetative growth (stems, petioles, and midribs) in the spring. The hairs are usually deciduous early in the growing season. They have short (0.1-0.2 mm), crisped rays and are never clustered or especially associated with vein axils. The fasciculate hairs found in all of our other species (except sometimes J . microcarpa ) are persistent, have longer (0.3-0.4 mm), straight rays, and are concentrated in clusters abaxially in the axils of the main lateral veins.