T r e e s  o f  N o r t h  C a r o l i n a

Acer L. (Sapindaceae)

A genus of about 111 species; primarily north temperate in distribution.

Eleven species occur in North Carolina, nine of which are considered native to the state.

Key to Acer in North Carolina

1. Leaves compound, divided into 3-7 (-9) leaflets...A. negundo (Boxelder)

1. Leaves simple, generally shallowly to deeply 3-5 (-7) lobed...2.

2. Leaves not toothed, or often with a few rounded, coarse, and irregular teeth on the principal lobes, these teeth 0-5 per principal lobe; sinuses between the principal leaf lobes generally broadly rounded, the sinus broader than deep...3.

3. Petioles and young twigs exuding milky sap when broken; inflorescence peduncled, the flowers on ascending, moderately stout pedicels; paired samaras held at >135° from one another; leaves 3-5-lobed, 4-8 (-10) cm wide...*A. campestre (Hedge maple)

3. Petioles and young twigs exuding clear sap when broken; inflorescence sessile, the flowers on drooping, filiform
pedicels; paired samaras held at <110° from one another...4.

4. Leaves pale, grayish, silvery-gray, or strongly glaucous beneath, glabrous, pubescent on the veins, or pubescent across the surface; leaf sinuses on either side of the terminal lobe deep, the two sides of each sinus forming an angle of < 70 degrees (the terminal lobe typically with parallel margins, or even narrower toward the base than toward the tip); leaves usually planar, but sometimes with drooping lobe tips, especially in A. floridanum, and especially in sun-exposed individuals...5.

5. Leaves small, (3.5-) avg. 8 (-11) cm broad; leaf undersurface usually pubescent; samaras 20-25 mm long; medium to large trees; bark gray, smooth and beech-like, becoming irregularly furrowed or plated in large individuals; [primarily of the CP and Pd]...A. floridanum (Southern sugar maple)

5. Leaves large, (8-) avg. 15 (-20) cm broad; leaf undersurface glabrous or pubescent only on the veins; samaras 25-30 mm long; large trees; bark grayish-brown, with loose-edged plates; [primarily of the Mountains and upper Piedmont]...A. saccharum (Sugar maple)

4. Leaves green beneath, moderately to densely pubescent across the surface; leaf sinuses on either side of the terminal lobe shallow, the two sides of each sinus forming an angle of >90 degrees (the terminal lobe typically broadly triangular); leaves sometimes planar, more usually with drooping lobe tips....6.

6. Leaves small, (3-) avg. 6 (-11) cm broad; small trees, often multi-trunked and crooked; bark whitish (in part because of dense growth of crustose lichens), becoming cracked and blackened on larger stems; [primarily of the Piedmont...A. leucoderme (Chalk maple)

6. Leaves large, (8-) avg. 15 (-20) cm broad; large trees, single-trunked; bark dark brown or blackish, becoming furrowed in large individuals; [primarily of the Mountains and westward]...A. nigrum (Black maple)

2. Leaves finely to coarsely toothed, the toothing often regular, the teeth 8-50 per principal lobe; sinuses between the principal leaf lobes generally sharp, forming a definite angle (or if rounded, then the sinus much deeper than broad)...7.

7. Leaves deeply lobed, the two sinuses on either side of the central lobe deep and narrow, approaching the midrib, the terminal lobe thus narrower at its base than at its middle; flowers either with petals (A. palmatum) or without petals (A. saccharinum)...8.

8. Leaves green beneath (or purple in many forms); main leaf lobes 5-9, these main lobes merely toothed or in some cultivars variously further divided; [small exotic tree, commonly planted and weakly naturalizing]...*A. palmatum (Japanese maple)

8. Leaves silvery white beneath; main leaf lobes 3-5, these main lobes with coarse teeth and smaller lateral lobes; [large native tree (also extensively planted)]...A. saccharinum (Silver maple)

7. Leaves shallowly lobed, the two sinuses on either side of the central lobe broadly wedge-shaped, not approaching the midrib, the terminal lobe thus broadest at its base and progressively (though often irregularly) narrowing toward the tip; flowers with petals...9.

9. Winter buds sessile, with 4-10 imbricate scales; inflorescence a sessile or subsessile cluster or fascicle; Samaras maturing in spring; leaves slightly to strongly glaucous-whitened beneath; medium to large tree (to 100 cm DBH)...A. rubrum (Red maple)

9. Winter buds stalked, with 2-4 valvate scales; inflorescence an elongate drooping raceme or erect panicle; petals green to bright yellow, 2-10 mm long; Samaras maturing in midsummer to autumn; leaves green beneath; shrub, small tree, or medium tree (to 35 cm DBH)...10.

10. Bark with narrow white stripes on a green background (best seen on stems 3-10 cm in diameter); leaf blades 12-20 (-30) cm long and wide, finely serrate (5-10 teeth per cm), pubescent beneath with yellow to orange hairs 0.1-0.3 mm long (as seen at 10× magnification); inflorescence a drooping raceme...A. pensylvanicum (Striped maple)

10. Bark brownish, never conspicuously striped; leaf blades 8-12 (-14) cm long and wide, coarsely serrate (2-3 teeth per cm), pubescent beneath with whitish hairs 0.3-1.0 mm long (as seen at 10× magnification); inflorescence an erect panicle...A. spicatum (Mountain maple)