A deciduous tree 30 to 40 ft high, with a trunk 12 to 18 in. in diameter, of rounded habit; branchlets at first minutely downy. Leaves 4 to 6 in. wide, not quite so long, deeply three-lobed, the lower pair of lobes usually again divided into two, but not deeply so; lobes ovate, with a long blunt apex, the margins cut into several large rounded teeth; stalks downy, as are also both surfaces, especially on the ribs and chief veins. On young trees the leaves are deeply notched at the base, but on older ones they are frequently truncate. Flowers yellow, downy, produced a few together each on a slender stalk in corymbs 2 to 3 in. long. Fruit with downy nutlets; keys 3⁄4 to 1 in. long; wings 1⁄3 in. wide, slightly reflexed beyond the horizontal position.
Native of Japan; sent to Kew in 1895 by Prof. Sargent, who had discovered this rare tree in September 1892, in a new locality in Yezo. He records the incident in the Forest Flora of Japan, p. 29:
‘We stopped quite by accident at Iwanigawa, a railroad junction in Yezo some 40 or 50 miles from Sapporo, and, having a few minutes on our hands, strolled out of the town to a small grove of trees. In this grove, occupying a piece of low ground on the borders of a small stream, and chiefly composed of Acer pictum, was A. Miyabei covered with fruit. The find was a lucky one, for Iwanigawa is a long way from the station where this maple had been discovered and mature fruit had not been seen before. From these trees I obtained later a supply of seeds, enough to make this maple common in the gardens of America and Europe.’
It is thriving well at Kew, where there is an example 37 × 21⁄4 ft, and is evidently well adapted for the English climate. Other specimens recorded are: Westonbirt, Glos., 46 × 31⁄4 ft (1966) and Batsford Park, Glos., 52 × 4 ft (1963). Of European maples A. platanoides is most closely related to it, and it has, like that species, milky juice in the leaf-stalks.