Northern Ontario Plant Database

Plant Description

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Fraxinus pennsylvanica Marshall

En: green ash, red ash, downy ash
Fr: frêne rouge d'Amérique
Oj: aagimaak

Oleaceae (Olive Family)

The Genus Fraxinus: Ontario's native ash species grow to be relatively tall trees. All species have opposite, deciduous, pinnately compound leaves with 5–11 leaflets, the terminal leaflet is stalked. Flowers are mostly unisexual, but bisexual (perfect) flowers may occur in the same inflorescence as unisexual flowers; flowers are borne in clusters (panicles) in the axils of the previous year's leaves. Petals are lacking; sepals are present in some species, but absent in black ash; stamens 2; the single pistil develops into a flat, winged samara.

General: A medium-size to tall tree, to 25 m tall. Bark gray to grayish-brown, furrowed; the stout twigs typically velvety-pubescent, or glabrous in var. subintegerrima (green ash); buds dark brown, conical; leaf scars hemispherical to oval, flattened and slightly concave along the upper margin; the bundle trace scars form a nearly-complete circle within the lateral leaf scars.

Leaves: Opposite to nearly opposite, pinnately compound, with 5–9 stalked leaflets. Leaflets are elliptic to ovate, 10–15 cm long, green above, paler but not obviously whitened beneath, lower surface of leaflets is hairy, or glabrous in var. subintegerrima (green ash); leaflets on short, hairy, winged stalks (petiolules), with the blade decurrent along the upper margin of the stalk; the stalk of the terminal leaflet is much longer than the stalks of the lateral leaflets; leaflet bases blunt (obtuse) to rounded, oblique; apices sharply pointed (acuminate); margins entire, undulate, or toothed (serrate). Leaves turn yellow to yellowish-brown in autumn.

Flowers: Unisexual, with male and female flowers occurring on separate trees (plants dioecious). Flowers borne in elongate clusters (panicles) in the axils of the previous year's leaves. Flowers have very small sepals, but petals are lacking. Flowers bloom at about the same time as the leaves are emerging.

Fruit: A winged samara, linear to narrowly oblanceolate, 4–7.5 cm long, 3–6 mm wide, the wing about twice the length of the enclosed seed. The wing narrowing towards and extending about half- way along the length of the seed.

Habitat and Range: Streambanks, bottomlands, open fields, and disturbed sites, flood-tolerant; often growing with willows and silver maple. Red ash is a temperate, eastern North American species that occurs throughout southern and eastern Ontario; it ranges only through the lower portions of northern Ontario.

Internet Images: The Fraxinus pensylvanica webpage from the Trees of Wisconsin website. Click on the smaller images to view larger, more detailed photos.

The Fraxinus pensylvanica webpage from the Virginia Tech Dendrology website, and the Fraxinus pensylvanica webpage from the USDA Silvics of North America website.

Similar Species: The buds and leaf scars of red and black ash, Fraxinus nigra, are similar; both have hemispherical or oval leaf scars that are flattened to slightly concave along the top margin. But the first pair of lateral buds in red ash (and white ash) is very close to the terminal bud, while in black ash, the first pair of lateral buds is separated from the terminal bud by a short internode.

Comparison of Fraxinus (ash) species native to northern Ontario

	Fraxinus americana (white ash)	Fraxinus pensylvanica (red or green ash)	Fraxinus nigra (black ash)
# of leaflets [typical # (range)]	5–9, usually 7		7–11
twigs	glabrous	velvety pubescent, or glabrous in var. subintegerrima	glabrous
lateral leaflets	stalked, strongly whitened beneath	short stalked, paler or pubescent beneath, but not strongly whitened	sessile, lower surface with rusty hairs on the veins
leaf scars	deeply notched or U-shaped	hemispherical
		generally flat to slightly concave along the upper edge	slightly concave along the upper edge
position of terminal and lateral buds	lateral buds situated close to the terminal bud		lateral bud separated from terminal bud
samara	narrowly oblanceolate, the wing 2-3 times the length of, and attached only at the top of, the enclosed seed	narrowly oblanceolate, the wing about 2 times the length of, and attached about half- way along, the enclosed seed	narrow-elliptic, blunt, the wing about equal to the length to the enclosed seed
habitat	upland forests	lowland forests, streambanks, fields, disturbed soils	swamps, wet sites

Several other webpages on black ash can be found at these sites:

The Fraxinus nigra (black ash) webpage from borealforest.org.

The Fraxinus nigra webpage from the Trees of Wisconsin website. Click on the smaller images to view larger, more detailed photos.

The Fraxinus nigra webpage from the Virginia Tech Dendrology website.

The Fraxinus nigra webpage from the USDA Silvics of North America website.

Other species that may be confused with ash are Acer negundo, the Manitoba maple or box elder, and Juglans nigra, the black walnut. Both webpages below are from the Trees of Wisconsin website. Click on the smaller images to view larger, more detailed photos.

The Manitoba maple, Acer negundo, is also known as the ash-leaf maple due to its opposite, pinnately compound leaves, which can be differentiated from those of ash by the 5 (rarely 7) lobed leaflets. Other differences include the shape of the leaf scars and the fruit. Like other maples, Acer negundo has narrow U- or V-shaped leaf scars with 3 bundle trace scars and a pair of winged samara, while ashes have hemispherical or thicker U-shaped leaf scars with numerous bundle trace scars and narrow unpaired samaras.

At first glance, Juglans nigra, the black walnut, may be confused with an ash also. It has pinnately compound leaves, but with more leaflets, 11– 15, and a large globose fruit (a tryma, which is a drupe with a dehiscent husk). The twigs of walnuts have chambered pith, while ashes have twigs with solid pith.

The Virginia Dendrology website also has a webpage on Juglans nigra.

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