A round-topped, deciduous tree about 30 ft high; branchlets covered with whitish hairs when young, becoming glabrous later. Leaves 4 to 7 in. wide and long, five-lobed, heart-shaped or almost truncate at the base, the lobes broadly ovate and with a few large teeth. When young, both surfaces, the margins and the leaf-stalk are thickly covered with whitish hairs; with age, these mostly fall away, but remain on the stalk, ribs and veins, and are scattered more or less over the lower surface. Flowers yellow, produced in April before the leaves in short pendulous corymbs from the joints of the previous year's wood; flower-stalk downy, 1 to 11⁄2 in. long. Fruit with numerous whitish, stinging bristles on the nutlets and a few on the wings; keys 11⁄4 in. long; wings oval, 2⁄5 in. wide.
Native of Japan; introduced by Maries for Messrs Veitch in 1880. It is quite hardy, and is one of the biggest-leaved of hardy maples; but Prof. Sargent observes that it has no bright autumn colour, and is one of the least ornamental maples in Japan. The curious specific name is said to refer to the two horn-like, persistent styles attached to the inner side of the nutlets between the wings.
There is a specimen 45 × 31⁄2 ft in the Main Drive at Westonbirt (1966).
f. purpurascens (Franch. & Sav.) Rehd. A. purpurascens Franch. & Sav. – Flowers purple; unfolding leaves and young fruits also purple. This form is probably of Japanese garden origin and much to be preferred to the type. At Kew the foliage turns red in the autumn.
From the Supplement (Vol. V)
It should have been mentioned that this species is dioecious.
specimens: Syon Park, London, three trees of almost the same size, the largest 35 × 33⁄4 ft (1981); Borde Hill, Sussex, pl. 1909, 30 × 33⁄4 ft (1974); Beauport, Sussex, 44 × 51⁄2 ft (1983); Hillier Arboretum, Ampfield, Hants, 40 × 31⁄4 ft (1980); Westonbirt, Glos., 50 × 31⁄2 ft (1980).
f. purpurascens – This occurs in the wild, and in both sexes. But in gardens a male clone is the commoner, and also the more decorative.
A. sinopurpurascens Cheng – This is the Chinese counterpart of A. diabolicum (A. purpurascens Franch. was the name once used for the Japanese species as a whole, though founded on a purplish-flowered specimen). It was introduced by Gordon Harris to his collection at Mallet Court.