1. Acer ginnala Maxim. (Amur maple, Siberian maple)

A. tataricum L. ssp. ginnala (Maxim.) Wesm.

Map 804

Plants monoecious, shrubs or small trees to 3(8) m tall with spreading branches, the bark of young trees more or less roughened and gray, eventually becoming separated into long thin plates on older trees. Twigs yellowish brown to brown, the winter buds ovate, pointed at the tip, with 2 or 4 overlapping outer scales usually obscuring 2 or more inner scales. Leaf blades 2–8 cm long, broadly triangular-ovate in outline, the undersurface lighter green than the green to bluish green upper surface, glabrous or hairy along the main veins, usually with 3 main lobes (rarely with 2 additional short lobes), these tapered to sharply pointed tips and with the sinuses angled or V-shaped, the lateral lobes cut 1/3–1/2 of the way to the base, the central lobe often longer than the lateral ones and broadest at or just above the base, the margins irregularly toothed (sometimes appearing doubly toothed). Inflorescences produced during or after expansion of the leaves; dense, narrow panicles from branch tips; the flowers individually short-stalked. Calyces 1.8–2.5 mm long, the sepals fused only at the very base, the 4 lobes oblong-elliptic, rounded at the tips, whitish green, the margins scarious and usually with a fringe of short, curly hairs. Petals 4, 1.5–2.0 mm long, narrowly spatulate to oblanceolate, yellowish white. Staminate flowers with (7)8 stamens inserted on the margin of a nectar disk. Pistillate flowers with the ovary densely hairy. Fruits dispersing mostly long after the leaves are mature, the samaras 2.0–3.5 cm long, glabrous or sparsely hairy, the wings 1.5–3.0 cm long, narrowly spreading, sometimes appearing parallel or nearly so. 2n=26. April–June.

Introduced, known thus far from only from Howell and Lincoln Counties (native of eastern Asia; naturalized sporadically in the northeastern U.S. west to Minnesota). Disturbed portions of mesic upland forests and old fields.

Vegetatively, A. ginnala can be difficult to distinguish from glabrescent individuals of A. rubrum. It may be distinguished by its more compact and usually shrubby growth form, as well as its winter buds with usually fewer observable bud scales. Amur maple was first reported for Missouri by Ebinger and McClain (1991), who documented an extensive population near Elsberry in fields and forests surrounding the Plant Materials Center of the Natural Resources Conservation Service. It is fairly widely cultivated in northeastern North America and Europe, but it appears to escape relatively uncommonly. In the autumn, the foliage turns a beautiful bright crimson color. A number of cultivars (mostly differing in leaf shape and coloration) exist and several poorly defined subspecies also have been described. Naturalized plants in the midwestern United States correspond to ssp. ginnala.