A tree over 50 ft high, with stout young shoots clothed, like the common stalk of the leaf, with glandular hairs. Leaves 11⁄2 to 2 (occasionally 3) ft long, composed of eleven to seventeen leaflets, which are oblong, taper-pointed, finely toothed, obliquely rounded or slightly heart-shaped at the base, 3 to 7 in. long, 11⁄2 to 2 in. wide, downy on both surfaces, especially beneath. Male catkins slender, up to 1 ft long. Fruits clustered on long racemes, roundish ovoid, 2 in. long, covered with sticky down; nut about 11⁄4 in. long, rounded at the base, pointed at the top, nearly glabrous, but with a prominent ridge at the union of the two halves.
Native of Japan and Sakhalin; introduced to Europe about 1860, by Siebold. It is abundant in the forests of Japan, and its nuts are valued as food there. In Britain it gives no promise of bearing fruit to any advantage, and in spite of the considerable period that has elapsed since its introduction, there are few large specimens in the country. It appears to differ from J. mandshurica chiefly in the apex of the leaflet being more abruptly tapered and shorter-pointed, and in the prominent ridge and smoother surface of the nut.
The best specimen of the Japanese walnut so far recorded in Britain grows in the Edinburgh Botanic Garden; pl. 1906, it measures 55 × 6 ft (1967). There are three examples at Batsford Park, Glos., planted by the first Lord Redesdale. The two largest are both 45 ft high with girths of 61⁄4 ft at 3 ft and 7 ft at 4 ft respectively (1963). Other examples recorded are: East Bergholt Place, Suffolk, 30 × 41⁄4 ft (1966); West Hill Nurseries, Winchester, 35 × 3 3⁄4 ft (1961); Glasnevin Botanic Garden, Dublin, Eire, 37 × 31⁄4 ft (1966).
var. cordiformis (Maxim.)Rehd. J. cordiformis Maxim. – Nuts thin-shelled, with a broad, heart-shaped base. This is not known in the wild. An example at Kew, pl. 1899, measures 47 × 31⁄2 ft (1956). It flowers freely and the male inflorescences are very striking, being almost yellowish green. The fruits occasionally mature. There is another of 40 × 4 ft in the Edinburgh Botanic Garden (1967).