Flowers polygamo-diœcious. Calyx colored, 5- (rarely 4–12-) lobed or parted. Petals either none or as many as the lobes of the calyx, equal, with short claws if any, inserted on the margin of the lobed disk, which is either perigynous or hypogynous. Stamens 3–12. Ovary 2-celled, with a pair of ovules in each cell; styles 2, long and slender, united only below, stigmatic down the inside. From the back of each carpel grows a wing, converting the fruit into two 1-seeded, at length separable samaras or keys. Embryo variously coiled or folded, with large and thin cotyledons.—Trees, or sometimes shrubs, with opposite palmately-lobed leaves, and small flowers. Pedicels not jointed. (The classical name, from the Celtic ac, hard.)
[*] Flowers in terminal racemes, greenish, appearing after the leaves; stamens 6–8.
1. A. Pennsylvánicum, L. (Striped Maple.) Leaves 3-lobed at the apex, finely and sharply doubly serrate, the short lobes taper-pointed and also serrate; racemes drooping, loose; petals obovate; fruit with large diverging wings.—Rich woods, Maine to Minn., and southward to Va., Ky., and Mo. June.—A small and slender tree, with light-green bark striped with dark lines, and greenish flowers and fruit. Also called Striped Dogwood and Moose-Wood.
2. A. spicàtum, Lam. (Mountain M.) Leaves downy beneath, 3- (or slightly 5-) lobed, coarsely serrate, the lobes taper-pointed; racemes upright, dense, somewhat compound; petals linear-spatulate; fruit with small erect or divergent wings.—Moist woods, with the same range as n. 1. June.—A tall shrub, forming clumps.
[*][*] Flowers in nearly sessile terminal and lateral umbellate-corymbs, greenish-yellow, appearing with the leaves.
3. A. saccharìnum, Wang. (Sugar or Rock M.) Leaves 3–5-lobed, with rounded sinuses and pointed sparingly sinuate toothed lobes, either heart-shaped or nearly truncate at the base, whitish and smooth or a little downy on the veins beneath; flowers from terminal leaf-bearing and lateral leafless buds, drooping on very slender hairy pedicels; calyx hairy at the apex; petals none; wings of the fruit broad, usually slightly diverging.—Rich woods, especially northward and along the mountains southward. April, May.—A large and handsome tree.
Var. nìgrum, Torr. & Gray. (Black Sugar-M.) Leaves scarcely paler beneath, but often minutely downy, the lobes wider, often shorter and entire, the sinus at the base often closed.—With the ordinary form; quite variable, sometimes appearing distinct.
[*][*][*] Flowers in umbel-like clusters arising from separate lateral buds, and much preceding the leaves; stamens 3–6.
4. A. dasycárpum, Ehrh. (White or Silver M.) Leaves very deeply 5-lobed with the sinuses rather acute, silvery-white (and when young downy) underneath, the divisions narrow, cut-lobed and toothed; flowers (greenish-yellow) on short pedicels; petals none; fruit woolly when young, with large divergent wings.—River-banks; most common southward and westward. March–April.—A fine ornamental tree.
5. A. rùbrum, L. (Red or Swamp M.) Leaves 3–5 lobed, with acute sinuses, whitish underneath; the lobes irregularly serrate and notched, acute, the middle one usually longest; petals linear-oblong; flowers (scarlet, crimson, or sometimes yellowish) on very short pedicels; but the smooth fruit on prolonged drooping pedicels.—Swamps and wet woods. April.—A small tree, with reddish twigs; the leaves varying greatly in shape, turning bright crimson in early autumn.