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Northern Ontario Plant Database
Plant Description
The Genus Acer
Sapindaceae (Soapberry Family)
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.
Comparison Chart of Acer species native to Northeastern Ontario
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 |
Key to Native and Naturalized Acer species in Northeastern Ontario
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) |
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