Aceraceae, the Maple Family
Trees or shrubs, with opposite, lobed or compound leaves and inconspicuous flowers; sepals about 5; petals the same number, or none; stamens 4-12; ovary 2-lobed, ripening into a pair of winged fruits.
| 1a. Leaves compound (tree; flowers appearing before the leaves) | Box Elder, Acer negundo. |
| 1b. Leaves simple (Maple) — 2. | |
| 2a. Shrubs or small trees; leaves 3-5-lobed; the lobes with regularly serrate margins (flowers greenish-yellow, appearing later than the leaves) — 3. | |
| 2b. Trees; leaves 3-7-lobed; margins of the lobes entire or incised, but never regularly serrate — 4. | |
| 3a. Leaves finely and sharply serrate; twigs smooth; bark conspicuously striped with white lines | Striped Maple, Acer pennsylvanicum. |
| 3b. Leaves coarsely and bluntly serrate; young twigs pubescent; bark not striped | Mountain Maple, Acer spicatum. |
| 4a. Angles between the leaf-lobes rounded (flowers greenish-yellow, appearing with the leaves) — 5. | |
| 4b. Angles between the leaf-lobes acute or obtuse, but not rounded (flowers purple, red, or yellowish, appearing before the leaves) — 6. | |
| 5a. Leaves glabrous beneath, or minutely pubescent on the veins | Sugar Maple, Acer saccharum. |
| 5b. Leaves downy beneath | Black Maple, Acer saccharum var. nigrum. |
| 6a. Middle leaf-lobe usually more than half the length of the leaf, narrowed at its base; broken twigs with a strong odor | Silver Maple, Acer saccharinum. |
| 6b. Middle leaf-lobe usually less than half the length of the leaf, its sides parallel or broadened at the base; broken twigs without strong odor | Red Maple, Acer rubrum. |