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Tree 10–18 m, 1.3 m dbh. Bark smooth, thin and light grey when young, becoming dark grey to brownish black, thick and deeply ridged, with irregular scales developing on the ridges. Branches stout and spreading, forming an open, rounded crown; they may become pendulous with age. Branchlets slender, with rufous hairs when young, becoming reddish brown and smooth with small lenticels, and silvery brown later; leaf scars large, triangular with rounded corners, suggesting a shark’s tooth in outline, and conspicuously pale. Leaves 22–32 cm long including petiole, with 9–15(–19) shortly stalked leaflets 4.5–10 × 1.5–4 cm, ovate to lanceolate, usually curved, long-acuminate at apex, tapering to rounded or unequal at base, margins coarsely toothed, yellowish green in colour, paler beneath, pubescent above when young but becoming smooth with scattered solitary hairs below, the rachis remaining pubescent with white hairs (var. major). Male catkins yellowish, slender, 12–20 cm long, each flower with 30–40 stamens; female flowers one to four. Fruits solitary or sometimes two, 2.5–3.5 cm diameter, globose to almost ovoid, with a small sharp point at apex, husk fibrous, densely hairy. Nuts globose, flattened at base, 2.5–4 cm diameter, dark brown to black, with deep, broad grooves in the thick shell; kernel large and sweet. Manning 1957, Elias 1980, Whittemore & Stone 1997. Distribution MEXICO: Chihuahua, Durango, Sonora, Sinaloa; USA: Arizona, New Mexico. Habitat Streamsides and floodplains, between 700 and 2300 m asl. The town of Nogales in Arizona is said to be named for the stands of this walnut tree that once grew there (Elias 1980). USDA Hardiness Zone 8–9. Conservation status Not evaluated. Illustration Elias 1980; NT412. Cross-references B475 (as J. microcarpa var. major), K193. Taxonomic note Juglans major is the name accepted by Manning (1957) and the authors of Flora of North America; European authors (Wijnands 1989) have adopted J. elaeopyren, but J. major has priority.
It is not clear when true Juglans major was introduced to Europe, as this short to medium-sized tree has been much confused, in gardens and by botanists, with the related J. microcarpa. The two species are genetically quite distinct (Stanford et al. 2000), with disjunct distributions, but they will hybridise. They can be distinguished by the following key characters.
Leaflets 9–15(–19), usually (1.5–)2–3.5 cm wide when mature; stamens 30–40; fruits 2.5–3.5 cm diameter
Leaflets (15–)17–23, usually 1.5(–1.7) cm wide or less; stamens 20–30; fruits not more than 2 cm diameter
Juglans major is considered to be less hardy than the daintier, more attractive J. microcarpa, and in cultivation should probably be given a warm sheltered site, but it seems to be happy in much of England, where there is a scattering of good specimens from Yorkshire southwards (TROBI). The tallest, at 18 m, but with a dbh of only 25 cm (in 2004) is at Thorp Perrow Arboretum, Yorkshire. A stouter specimen at Cambridge Botanic Garden was measured at 17.5 m tall (69 cm dbh) in 2002; this was planted in 1923. At Kew a tree planted in 1982 had reached 5.5 m by 2004 and appears to be growing strongly, without evidence that it has suffered any frost damage.