3. Acer rubrum L. (red maple)

Pl. 196 c–f; Map 806

Plants monoecious or dioecious, small to medium trees to 15 m tall with usually spreading branches, the bark of young trees smooth and gray, eventually becoming dark gray to brown and separated into long thin plates or ridges on older trees. Twigs red and shiny, the winter buds ovate, bluntly pointed at the tip, with 4–10 overlapping scales. Leaf blades 5–12 cm long, broadly triangular-ovate to nearly semicircular in outline, the undersurface lighter than the green to dark green upper surface and often strongly white-glaucous, glabrous or hairy, with 3 or 5 main lobes, these tapered to sharply pointed tips and with the sinuses angled or V-shaped, the lateral lobes cut 1/4–1/2 of the way to the base, the central lobe shorter than to slightly longer than the lateral ones and broadest at or just above the base, the margins irregularly toothed (sometimes appearing doubly toothed). Inflorescences produced before the leaves, dense clusters from lateral buds along the branches, the flowers sessile or nearly so (the stalks elongating greatly after flowering as the fruits mature). Calyces 1.4–2.2 mm long, the sepals fused only at the very base, the 4 or 5 lobes oblong-elliptic, rounded at the tips, red to purplish red, glabrous, the margins not scarious. Petals 4 or 5, 1.6–2.4 mm long, narrowly oblong to linear, orangish red to purplish red. Staminate flowers with 5–8 stamens inserted on the margin of a nectar disk. Pistillate flowers with the ovary glabrous. Fruits dispersing mostly after the leaves are mature, the samaras 2–4 cm long, glabrous, the wings 1.5–3.0(–4.0) cm long, narrowly spreading, sometimes appearing parallel or nearly so. 2n=78, 91, 104. March–April.

Scattered to common in the Ozark, Ozark Border, and Mississippi Lowlands Divisions (eastern U.S. west to Illinois, Missouri, and Texas; Canada). Swamps, bottomland forests, mesic to dry upland forests, sinkhole ponds, banks of streams, and ledges of bluffs.

Acer rubrum has been considered a minor component of most forest ecosystems in which it occurs. However, Abrams (1998) has documented an explosive increase in the abundance of this species throughout much of its range during the past several decades that is analogous to the situation apparent in Missouri for A. saccharum. Abrams attributed this to an opportunistic increase of the species resulting from the cumulative effects of land management patterns in the region, including logging practices, land clearing for agriculture, diseases of other forest trees, and fire suppression.

In addition to the use of its wood for veneers, implements, furniture construction, and pulp for papermaking, as well as the use of its sap as a low-grade substitute for that of sugar maple in syrup production, red maple has also been used historically as a source of tannins for ink production, and an extract of the bark was used for preparing reddish brown and black dyes (Steyermark, 1963). The leaves turn a bright crimson to orangish red color in the autumn and the species is cultivated as an ornamental for its foliage. The species is highly variable in leaf size, shape, and coloration. Some forms with 3-lobed leaves have been segregated as var. trilobum, but as noted by Steyermark, there is no correlation between this character and others involving fruit size and leaf pubescence. In Missouri, two ecologically distinctive but morphologically overlapping varieties may be recognized. Plants in flower (prior to the development of leaves) cannot be separated into varieties based on morphology, although the habitat in which a tree is growing may provide clues, as var. drummondii is unknown from upland sites in Missouri.