A small, deciduous tree, sometimes a shrub. Leaves five-lobed, 2 to 31⁄2 in. long and wide, glabrous except for a tuft of hairs at the base, where the ribs join the stalk; base heart-shaped; lobes ovate with a long drawn-out point, deeply and handsomely toothed; leaf-stalk downy. Flowers greenish white, numerous, on slender racemes 11⁄2 to 3 in. long, small (about 1⁄5 in. across). Fruits glabrous; keys 1⁄2 to 1 in. long; wings 1⁄4 in. wide, rounded at the end, spreading at a wide angle.
Native of Japan; introduced about 1879. The foliage turns a bright red in autumn, and is very prettily cut. It belongs to the same group of maples as A. rufinerve and A. capillipes, but within that group its nearest ally is A. tschonoskii, from which it differs in its small flowers, which are also more numerous on each raceme than in the other species (ten or more).
From the Supplement (Vol. V)
This admirable species is still uncommon in cultivation, but becoming more widely planted for its elegant foliage and its splendid red autumn colour. Among the oldest trees in gardens are those that grow at Crarae, Argyll, and Methven, Perthshire. The young examples in the Hydon Nursery near Godalming, Surrey, are propagations from one that grew at Tower Court, Ascot. For an illustrated note on A. micranthum, see Journ. R.H.S., Vol. 100 (1975), p. 92 and fig. 30.
With its quite deeply palmately lobed foliage A. micranthum could, in the absence of flower or fruit, be taken for an ally of A. palmatum. It is in fact a member of the snake-bark group of maples (sect. Macrantha), and is akin to A. tschonoskii.