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
Twigs	glabrous	glabrous	glabrous	glabrous	finely hairy
Number of bud scales	6—8 pairs, imbricate	4 pairs, imbricate	4 pairs, imbricate	2 valvate scales	2 valvate scales
Number of leaf lobes	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
Shape of central leaf lobe	shouldered, with nearly parallel sides	shouldered, with nearly parallel sides	shouldered, narrowed at the lobe base	triangular	triangular
Leaf margin in sinus between lobes	entire	coarsely serrate	entire	finely double serrate	coarsely serrate
Flowers	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
Sepals	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
Petals	absent	red, small, about equal in size to sepals	absent	yellow-green, obovate, to 6 mm long	white, linear-oblanceolate, 4—5 mm long
Samaras	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
Angle of sinus between paired samaras	>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
Most distinctive traits	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)

Back to species list