Key to the Maples of Iowa

1. Leaves compound; flowers unisexual, the trees dioecious [bearing either male or female flowers, but not both]. Acer negundo
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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