| 1. | Leaves compound; flowers unisexual, the trees dioecious [bearing either male or female flowers, but not both]. | Acer negundo Boxelder |
| 1. | Leaves simple; flowers perfect or polygamous [perfect and unisexual flowers on same plant], the trees monoecious. | [2] |
| 2. | Leaves strongly whitened beneath; flowers in dense clusters on the twigs before the leaves emerge. | [3] |
| 2. | Leaves green beneath; flowers various arranged. | [4] |
| 3. | Sinus between terminal and lateral leaf lobes V-shaped at the base, opening wide; flowers stalked, petals present and ± equal in length to sepals . | Acer rubrum Red maple |
| 3. | Sinus between terminal and lateral lobes U-shaped at the base, the sides nearly overlapping above; flowers nearly sessile, petals lacking. | Acer saccharinum Silver maple |
| 4. | Leaf margins with numerous small teeth; leaves unlobed or 3-lobed, usually distinctly longer than wide. | [5] |
| 4. | Leaf margins coarsely toothed; lobes usually 5-7. | [6] |
| 5. | Mature bark shaggy, splitting vertically into long loose plates; leaves typically 3-lobed [sometimes unlobed] with center lobe much longer than the lateral two, lower leaf surface pubescent; twigs of current year pubescent; terminal buds with 2 opposite scales. | Acer spicatum Mountain Maple |
| 5. | Bark ridged to deeply furrowed; lower leaf surface glabrous; leaves typically 3-lobed [sometimes 5-lobed] lobes ± equal; twigs of current year glabrous; terminal buds w/≥ 4-scaled. | Acer ginnala Amur Maple |
| 6. | Wings of fruit diverging at nearly 180 degrees; flowers borne in a panicle, petals present; petioles exuding milky juice when broken. |
Acer platanoides Norway maple |
| 6. | Wings of fruit diverging at about 90 degrees; flowers borne in fascicles from winter buds, on slender drooping stalks, petals lacking; juice not milky. | [7] |
| 7. | Undersides of leaves downy; leaf margins drooping; leaves usually with 3 prominent lobes. | Acer nigrum Black maple |
| 7. | Undersides of leaves glabrous; leaf margins not drooping; leaves usually with 5 prominent lobes. | Acer saccharum Sugar maple |
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| "When you have seen one ant, one bird, one tree, you have not seen them all." --- E. O. Wilson |