A slender tree 20 to 30, sometimes 50 ft high in Japan, belonging to the Ornus section; young shoots soon glabrous, grey. Leaves ordinarily 4 to 6 in. long; leaflets usually five (rarely seven), which are 11⁄2 to 4 in. long, 3⁄4 to 11⁄2 in. wide, ovate to obovate, tapered at the base, the apex abruptly contracted into a slender point, toothed or almost entire, glabrous above, downy only at the sides of the midrib near the base beneath or sometimes quite glabrous beneath. The terminal leaflet, which is the largest, has a stalk 1⁄2 to 3⁄4 in. long, the uppermost pair are stalkless, the lower pair or pairs shortly stalked; common stalk grooved on the upper side. Flowers white, in terminal and axillary panicles 3 to 5 in. long, produced in June. Petals four, about 1⁄4 in. long. It is the Japanese representative of F. ornus, differing most obviously in the few leaflets.
This ash is usually called F. longicuspis, but according to Ohwi’s Flora of Japan (1965) the species so named by Siebold and Zuccarini has flowers without petals and differs in other respects also from the plant described above. This conclusion is no doubt based on an examinaton of the type specimen.
F. lanuginosa Koidz. – This is said to be very near to F. sieboldiana, differing in having the young stems, petioles, and inflorescences either quite glabrous or clad with short, spreading, rather bristly hairs.