Juglans californica
Juglans microcarpa
California black walnut, Southern California black walnut, Southern California walnut
little walnut, namboca, nogal, nogalito
with distal edge of leaf scar notched, often shallowly so, glabrescent or bordered by poorly defined velvety patch;
pith brown.
with distal edge of leaf scar notched, glabrous or bordered by poorly defined velvety zone;
pith light to dark brown.
15-24 cm;
petiole 2-5 cm.
12-29 cm;
petiole 1-3(-4) cm.
(9-)11-15(-17), usually narrowly oblong-elliptic to lance-elliptic, occasionally lanceolate, symmetric or weakly falcate, 4.3-9.5 × 1.6-2.6 cm, margins finely serrate, apex rounded to acute;
surfaces abaxially without tufts of hair in vein axils, abaxially and adaxially glabrous with scales but no hairs, main veins glandular, often sparsely so, leaflets without nonglandular hairs (except for multiradiate hairs early in season);
terminal leaflet well developed.
17-25, lanceolate or narrowly lanceolate, weakly to strongly falcate, 5.2-6.3(-9.6) × 0.8-1.1(-2.2) cm, margins entire or toothed, apex long-acuminate;
surfaces abaxially with capitate-glandular hairs (sometimes becoming sparse late in season except along veins), often scattered scales, axils of proximal veins usually, not always, with prominent tufts of fasciculate hairs, adaxially with capitate-glandular hairs (late in season hairs sometimes becoming sparse except along veins);
terminal leaflet usually small.
1-3, globose, 2.1-3.5 cm, smooth, at first glandular, with scattered scales, soon glabrescent;
nuts depressed-globose, 1.8-2.2(-2.5) cm, shallowly grooved, surface between grooves smooth.
1-3, globose, 1.4-2.3 cm, smooth, with capitate-glandular hairs;
nuts globose to depressed-globose, 1.1-1.7 cm, grooved, surface between grooves smooth.
buds ovoid to ellipsoid, somewhat flattened, 5-6 mm.
buds globose to short-ovoid, not flattened, 3-5 mm.
catkins 5-14 cm;
stamens 15-35 per flower;
pollen sacs 0.6-1 mm.
catkins 3-7 cm;
stamens 20-25(-35) per flower;
pollen sacs 0.8-1 mm.
Juglans californica
Juglans microcarpa
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.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
Specimens of Juglans microcarpa with larger leaflets (parenthetical numbers above) may result from introgression with J. major. These have sometimes been treated as J. microcarpa var. stewartii (I. M. Johnston) W. E. Manning, but W. E. Manning (1978) reported this variety only from Mexico. Intermediates between J. microcarpa and J. nigra (q.v.) are also known.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
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