Maples are tall shrubs or trees with opposite, deciduous leaves. Most maples have simple, palmately-lobed leaves, with the exception of Acer negundo (Manitoba maple or box elder), which has pinnnately compound leaves. Most have buds with overlapping (imbricate) bud scales and narrow V- or U-shaped leaf scars with 3 bundle scars. The small bisexual or unisexual flowers have 5 sepals, 5 petals, 10 stamens and/or a 2-carpelled ovary surrounded at the base by a nectar-producing disk; the ovary develops into a pair of indehiscent, winged samaras, commonly called maple "keys", which are wind-dispersed. Some maple species are bisexual, others have both male and female parts in the same flower, but only one sex is functional.
| Trait/Species | Acer saccharum | Acer rubrum | Acer saccharinum | Acer pensylvanicum | Acer spicatum |
| glabrous | glabrous | glabrous | glabrous | finely hairy |
| 6—8 pairs, imbricate | 4 pairs, imbricate | 4 pairs, imbricate | 2 valvate scales | 2 valvate scales |
| 5, basal 2 lobes smaller |
3—5; basal 2 lobes smaller if present |
usually 5; sometimes with 2 smaller basal lobes |
usually 3, sometimes with 2 much smaller basal lobes |
usually 3, sometimes with 2 much smaller basal lobes |
| shouldered, with nearly parallel sides |
shouldered, with nearly parallel sides |
shouldered, narrowed at the lobe base |
triangular |
triangular |
| entire |
coarsely serrate |
entire |
finely double serrate |
coarsely serrate |
| monoecious; in drooping sessile clusters; pedicels hairy, elongating to 3—7 cm |
monoecious; male flowers in nearly sessile clusters; female and perfect flowers in sessile umbels |
monoecious; male flowers in nearly sessile clusters; female and perfect flowers in sessile umbels |
dioecious; in pendant racemes |
monoecious; in erect narrow panicles |
| yellow-green, tubular, 4—6 mm long |
red, small, about equal in size to petals |
yellow-green to somewhat reddish, small |
yellow-green, fused into a small calyx |
greenish, fused into a calyx , 1—2 mm long |
| absent |
red, small, about equal in size to sepals |
absent |
yellow-green, obovate, to 6 mm long |
white, linear-oblanceolate, 4—5 mm long |
| each 2.5—4 cm long; glabrous; seedcase plump, not indented |
each 1.5—5 cm long; red, glabrous |
each 4—7 cm long; hairy when young; seedcase prominently veined |
each 2—3.3 cm long; glabrous, seedcase indented on one side |
each 1.5—2.5 cm long; glabrous, seedcase indented on one side |
| >90°; U-shaped open sinus |
45°—90°; V-shaped narrow sinus |
about 90°; V-shaped broad sinus |
about 90°; U-shaped open sinus |
<90° wide; V-shaped narrow sinus |
| leaves broadly 5-lobed, with entire sinuses between lobes |
flowers red, in sessile clusters; samaras red |
first maple to bloom; base of central leaf lobe narrowed at the base |
bark striped; flowers in pendant racemes |
flowers in erect narrow panicles |
| 1a. | Leaves compound, with 3—7 leaflets; introduced in the Algoma District, restricted mainly to city streets and disturbed areas. |
Acer negundo (Manitoba maple, box elder) |
| 1b. | Leaves simple, palmately 3—5 lobed; native in forested areas of the Algoma District. |
go to 2 |
| 2a. |
Leaves with a triangular central lobe, tapering gradually to the apex; buds with 2 valvate scales. | go to 3 |
| 2b. |
Leaves with a shouldered central lobe, tapering in a step-like fashion to the apex; buds with 4—8 pairs of imbricate scales. |
go to 4 |
| 3a. | Leaf surface flat, margins finely double-serrate; flowers in pendant racemes with conspicuous yellow-green petals; bark green, marked with vertical white to dark (at maturity) stripes; twigs and buds glabrous. |
Acer pensylvanicum (striped maple) |
| 3b. | Leaf surface rugose, with impressed veins, margins coarsely toothed; flowers in erect to arching panicles, with inconspicuous narrow pale green to white petals; bark not striped; twigs and buds finly hairy. |
Acer spicatum (mountain maple) |
| 4a. |
Margins between leaf lobes entire. |
Acer saccharum (sugar maple) |
| 4b. |
Margins between leaf lobes serrate. |
go to 5 |
| 5a. | Indentations between upper leaf lobes deep, usually cut more than half-way to the midrib; the central lobe has concave to nearly parallel sides, usually distinctly narrower at the base of the lobe; sinuses are narrow, less than 45° wide; ovaries and young fruit are hairy. |
Acer saccharinum (silver maple) |
| 5b. | Indentations between upper leaf lobes shallow, usually cut less than half-way to the midrib; the central lobe has straight to nearly parallel sides, only slighly narrower, if at all, at the base of the lobe; sinuses are broad, generally between 45°—90° wide; ovaries and young fruit are glabrous. |
Acer rubrum (red maple) |