Acer japonicum, the Amur maple, downy Japanese-maple or fullmoon maple; Japanese: ハウチワカエデ hauchiwakaede) is a species of maple native to Japan, on Honshū, Hokkaidō, Kyūshū (Nagasaki Prefecture), and also southern Korea.Acer japonicum is a small deciduous tree growing to 5–10 m (rarely 15 m) tall, with a trunk up to 40 cm in diameter. The bark is smooth on young trees, becoming rough and scaly on old trees. The shoots are slender, and thinly downy with whitish hairs. The leaves are rounded, 7–15 cm in diameter with 9–13 (rarely 7) serrate lobes incised to half or less of the diameter of the leaf; they are downy at first with white hairs, the hairs mostly lost by late summer except on the veins and the underside of the leaf; the petiole is 2–4 cm long and hairy. In autumn, the leaves turn bright orange to dark red. The flowers are 1 cm in diameter, dark purplish-red with five sepals and petals; they are produced 10–15 together in drooping corymbs in early spring as the leaves start to open. The fruit is a paired samara with the nutlets 7 mm in diameter with a 20–25 mm wing, hanging under the leaves.
The closely related species Acer shirasawanum (Japanese, オオイタヤメイゲツ ooitayameigetsu) from southern Japan is sometimes included as a subspecies of A. japonicum. It is distinct in its hairless shoots, and usually smaller leaves. Another related species, Acer sieboldianum (Japanese: コハウチワカエデ kohauchiwakaede), is best distinguished by its yellow (not red) flowers, and smooth bark even on old trees. It is more easily distinguished from Acer palmatum, as that species rarely has leaves with more than seven lobes.