Recognizing ash trees in Oregon, Washington and Northern California

About 70 species of ash grow in the world, and about 16 are native to North America. Only one, Oregon ash, Fraxinus latifolia, is native to the Northwest. Many others are common landscape and roadside plantings, notable for their bright yellow to red fall foliage. All ash trees are susceptible to emerald ash borer, an invasive pest first sighted in Oregon in June 2022. The insect was introduced to Michigan in about 2002 and has spread rapidly, causing extensive mortality of all native ash species.

Browse the galleries below to learn about:

Ashes in general
Our only native ash, Oregon ash
Several of the predominant non-native ash and ash cultivars (a cultivar is a plant that people have bred for desired traits)
Trees that might be confused with ashes
Common riparian trees in Oregon that grow in association with Oregon ash

Ash (Fraxinus) in general

About ash

Figure 1a. Pinnately compound leaf.

Photo: Patrick Breen
Figure 1b. Simple leaf.

Photo: Patrick Breen
Figure 2a. Opposite leaf arrangement.

Photo: Patrick Breen
Figure 2b. Alternate leaf arrangement.

Photo: Patrick Breen
Figure 3. A samara.

Photo: Patrick Breen

Ashes are easy to identify because they’re one of the few groups of trees whose leaves are both opposite and pinnately compound — that is, a complete leaf is composed of a single stalk with multiple leaflets arising along that stalk (Figure 1); and pairs of complete leaves arise oppositely from one another on the branch (Figure 2). Fruits are dry, single-winged seeds (samaras) that are shaped like canoes (Figure 3). Some say it’s because ashes grow near water and their seeds are designed for floating. Ashes lose their leaves in winter — that is, they are deciduous.

Oregon is home to one native ash tree

Oregon ash (Fraxinus latifolia)

Figure 4. Oregon ash tree.

Photo: Patrick Breen
Figure 5. Oregon ash leaves, oppositely arranged.

Photo: Patrick Breen
Figure 6. A cluster of samaras with leaves.

Photo: Patrick Breen

Has a narrow, dense crown arising from a single straight trunk (Figure 4), although multiple trunks are also common.
Leaves are opposite and pinnately compound; one complete leaf is commonly 5–10 inches (15–30 cm) long (Figure 5).
Each complete leaf has five to seven oval leaflets, each 2–5 inches (5-15 cm) long and 1–1.5 inches (2.5–4 cm) wide. They are elliptical, with a short-pointed terminal end.
The lateral leaflets are stalkless, or on a short stalk (petiolule). They are medium to light green above and paler green and slightly hairy below. Fall color is yellow or brown.
Fruits are single samaras about 1 inch long (each looks like half a maple seed) that hang in dense clusters. They spin in the wind when they are dispersed (Figure 6).
Oregon ash grows in sun or part shade.
Oregon ash dominates seasonal wetlands in western Oregon lower elevation valleys and is a common streamside tree in mixed forests.
Oregon ash is native to western portions of Washington and Oregon, and from south in the Coast Range and Sierra Nevada to Central California.

Common non-native ash trees in Oregon

White ash or American ash (Fraxinus americana)

Figure 7. American ash tree

Photo: Patrick Breen
Figure 8. American ash leaf

Photo: Patrick Breen

Grows 50-80 ft (15-24 m) tall (Figure 7).
Leaves are opposite and pinnately compound; 8–15 inches (20-38 cm) long (Figure 8).
Each leaf has 5–9 lateral leaflets (usually 7), each 2–5 inches (5–15) cm long; the edge of the leaflets may be slightly jagged. The upper portion of each leaflet is smooth and shiny, but there may be hairs on the major veins on the underside of the leaf.
Fall color ranges from yellow to maroon to deep purple.
Fruits are single-winged samara, 1-2 inches (2.5–5 cm) long.
This ash prefers full sun.
Grows best in deep, moist, well-drained soil. Fall color is better in full sun.
This tree ranges from Nova Scotia west to Minnesota and south to Florida and Texas.

Green ash (Fraxinus pennsylvanica)

Figure 9. Green ash tree

Photo: Patrick Breen
Figure 10. Leaf of green ash

Photo: Patrick Breen

Grows to 50-60 ft tall and up to 40 ft wide, (15-18 m × 14 m), developing a spreading habit at maturity (Figure 9).
Each complete leaf is pinnately compound and opposite, with 5-9 (usually 7) leaflets (Figure 10).
Leaflets may be jagged along their edges. Upper surfaces are smooth, while the underside is hairy. Leaflets are dark green and hairless above, but pubescent (hairy) below (sometimes only on major veins).
Fall color is yellow, golden, or bronzy.
Fruits are samaras; 1 – 2 inches (2.5-5 cm) long and the wing extends about halfway down the fruit.
This tree grows well in full sun, tolerates a wide variety of soils, and is a popular street and landscape tree.
The native range of the species extends from Nova Scotia to Manitoba, south to Florida and Texas (including Pennsylvania, hence the scientific name of pennsylvanica).

European ash or common ash (Fraxinus excelsior)

Figure 11. European ash tree

Photo: Patrick Breen
Figure 12. European ash leaf

Photo: Patrick Breen

Grows to 85-100 ft (25-30 m] tall and an equal or even somewhat greater width. Its crown is broad spreading and rounded (Figure 11).
Its leaves are opposite and pinnately compound, with seven to 11 leaflets (Figure 12). Each complete leaf is 10-12 inches (25-30 cm) long.
The edges of the leaflets are jagged and the leaflets have a distinct, elongated tip.
Fall color is green to yellow (Figures 5-6).
Winter buds are black, or nearly so
Fruits are winged samaras, 1-2 in (2.5-4 cm) long; the tip of each samara is tip rounded to pointed.
Grows in sun.
This species is native to the British Isles, Europe and Caucasus, and has been cultivated for centuries.

Raywood ash (Fraxinus oxycarpa)

Figure 31. Raywood ash tree.

Photo: Patrick Breen
Figure 32. Raywood ash leaf.

Photo: Patrick Breen
Figure 33. Raywood ash tree fall color.

Photo: Patrick Breen

Raywood ash is the most commonly planted ash cultivar in landscapes and roadsides (Figure 31).
Leaves opposite, but often whorls of 3 or 4 at ends of branches, pinnate compound, 25-30 cm long, 7 to 9 leaflets (Figure 32).
A small stature tree, grows to 30 or 40 ft (9-12 m) tall.
Fall color beautiful red (Figures 33).

Look-alikes to ash trees

All of these look-alike trees have pinnately compound leaves, but most have an alternate leaf arrangement (except box elder and elderberry). Ashes have an opposite leaf arrangement which can be used to help distinguish most of these from ash.

Black and English walnut (Juglans nigra, Juglans regia)

Figure 13. Leaf of black walnut vs. English walnut

Photo: Patrick Breen
Figure 14. Winter twig showing buds that alternate along the stem

Photo: Patrick Breen

Black walnut is commonly planted along streets and in parks, and also in orchards. It commonly grows into a very large tree.
English walnut is the primary commercial walnut and is much smaller at maturity than black walnut. They are often grafted onto the same stem.
Both have pinnately compound leaves (Figure 13) that are arranged alternately.
Leaves look similar to ashes but are arranged alternately along the stem (Figure 14).
Seeds are classic walnuts in a round, leathery husk.

Black locust (Robinia pseudoacacia) and Honeylocust (Gleditsia triacanthos)

Figure 15. Leaves of black locust vs. honeylocust.

Photo: Patrick Breen
Figure 16. Black locust seed pods.

Photo: Patrick Breen

A look-alike to ash trees, Black locust is common in roadside plantings and along fence lines.
Honeylocust is a common landscape tree. The cultivar has no thorns.
Both have pinnately compound leaves that are alternate on the stem (Figure 15).
Both may have thorns, but they are much more common in black locust.
Both have distinct, pea-like seed pods (Figure 16). Those of honeylocust are much larger than those of black locust.

European mountain-ash (Sorbus aucuparia)

Figure 17. Leaves and flowers of European mountain-ash.

Photo: Patrick Breen

This is not a true ash — it has alternately arranged compound leaves, and a fleshy, berry-like fruit. In Europe, it is commonly called rowan.
This tree/shrub is extensively planted in urban and suburban areas.
The tree is in the rose family and has distinct white flowers (Figure 17).
Leaves are pinnately compound but alternate, rather than opposite. Its leaflets are jagged along the edge (Figure 17), much more-so than most ashes.
Its fruits vary from orange to red and are commonly called berries, although they are actually apple-like.

Tree-of-heaven (Ailanthus altissima)

Figure 18. Photo of tree of heaven.

Photo: Patrick Breen
Figure 19. Photo of leaf of tree of heaven.

Photo: Patrick Breen
Figure 20. Photo of tree of heaven samara clusters.

Photo: Patrick Breen

The tree-of-heaven is an invasive tree that can grow to 40–60 ft (12-18 m) tall, but can also be shrubby. (Figure 18). It is known for its hardiness in urban areas.
It has large pinnately compound leaves 24 inches (60 cm) long (Figure 19).
Each leaflet has a jagged margin at the base of the leaf.
The fruit is a samara with the seed is in the middle of its wing (Figure 20).
The tree is present in urban areas generally, but in the eastern U.S. has become invasive in wildlands. Do not confuse it with an ash tree.

Sumac (Rhus species)

Figure 21. Staghorn sumac shrubs with fall colors.

Photo: Patrick Breen
Figure 22. Staghorn sumac leaf.

Photo: Patrick Breen
Figure 23. Red flower cluster of sumac.

Photo: Patrick Breen

There are a number of sumac species; many are used as ornamentals. It can be a look-alike to ash trees.
Sumacs are small trees or large shrubs and often grow in groups because they sprout from underground roots and stems (Figure 21).
Grows to 15 ft (4.5 m) tall.
Have alternate pinnately compound leaves (Figure 22).
Flowers occur in dense terminal clusters which are red (Figure 23).

Boxelder (Acer negundo)

Figure 24. Boxelder tree.

Photo: Patrick Breen
Figure 25. Boxelder leaf.

Photo: Patrick Breen
Figure 26. Boxelder samara.

Photo: Patrick Breen

Not to be confused with ash, the boxelder is a species of maple that defies several common maple characteristics. It is typically a small tree 30–50 ft (9-15 m) tall, and is often multi-stemmed.(Figure 24).
Like most other maples, it has opposite leaves. But unlike most, they are pinnately compound, rather than simple. They typically have three to five leaflets (Figure 25).
Their fruit is a double samara (Figure 26).
They are not native to Oregon, but they are invasive and show up in many spots, most often along rivers or lakes.

Golden raintree (Koelreuteria paniculata)

Figure 27. Photo of golden raintree in full flower.

Photo: Patrick Breen
Figure 28. Golden raintree leaf.

Photo: Patrick Breen

Another look-alike to ash trees, the Golden raintree is a small ornamental tree, often planted for its golden chains of flowers (Figure 27). Note that all parts of the plant are toxic to humans.
It has alternate, pinnately compound leaves with seven to 17 leaflets (Figure 28).
Leaflets have jagged edges.
Distinctive yellow flowers hang in long clusters.
The seeds are enclosed inside a papery bladder.

Elderberry (Sambucus)

Figure 29. Red elderberry.

Photo: Patrick Breen
Figure 30. Red elderberry leaf.

Photo: Patrick Breen

There are two native elderberries in Oregon: red and blue.
Black elderberry is not native, but also a common horticultural species in Oregon.
Red elderberry is most common on the west side of the Cascades (Figure 29). Red elderberries are described as toxic if eaten raw.
Elderberries typically grow as shrubs, with distinctive white flowers and berries (red or bluish).
Elderberries are easily confused with ashes because their leaves are pinnately compound and opposite (Figure 30).

Additional information

Common riparian trees in the Pacific Northwest

- Red alder
- White alder
- Big leaf maple
- Black cottonwood
- Cascara
- Oregon white oak
- Oregon ash
- Willamette Valley ponderosa pine
- Western redcedar
Photo taken by Dustin Johnson

Resources useful for identifying trees in Oregon

- Trees to Know in Oregon and Washington by Edward C. Jensen (OSU Extension Service EC 1450)
- OSU Department of Horticulture website (Patrick Breen) (all the photos in this guide were taken from this website)
- The Sibley Guide to Trees. David A. Sibley. 2009. Alfred A. Knopf, Inc. New York.
Special thanks to Ed Jensen for comments and review, and to Patrick Breen for photos used in this gallery.

Photo: Dave Shaw