Fraxinus latifolia - Oregon Ash

Family: Oleaceae
Wetland Indictor Status: FACW

General Species Description

F. latifolia is a tall, deciduous tree that grows to 10-20 m in length and up to 1 m in diameter. In some rare instances old-growth specimens of this native tree- the only ash native to the Northwest- can reach up to 2 m in diameter. The often long, straight trunk has rough grayish brown bark that is deeply vertical-ridged in mature trees creating a diamond or diagonal pattern. Twigs are round and stout, 3-5 mm in diameter, green to grayish in color and slightly hairy.


Leaves are opposite and pinnately compound, usually about 13-30 cm in length. Leaflets number 5 or 7, sometimes 9, are opposite except at end, oblong to oblong-ovate, and may reach up to 15 cm. They are stalkless, light green above, paler and hairy below, usually with smooth margins. They turn yellow or brown in the fall.


Inconspicuous male and female flowers are found on separate trees March to May. Yellowish male and greenish female flowers reach 3mm in length.


Fruits of F. latifolia are long, simple-winged samaras 3-5 cm long, which hang in dense bunches and mature in early fall.


Typically found in wetland habitats (ie. Wooded wetlands, lakeshores, along lowland streams) along with red alder (Alnus rubra), black cottonwood (Populus balsamifera), willows (Salix species), redstem dogwood (Cornus sericea), Pacific ninebark (Physocarpus capitatus), and cascara (Rhamnus purshiana).


Found along the coast from British Columbia south past San Francisco and inland to the Cascades. In Northwestern Oregon this species stretches from the northwesternmost counties (Clatsop, Columbia and Clark) south past Lane county.

Similar Species

A. rubra, P. balsamifera and some Salix species are associated species that may be confused with F. latifolia at first glance, but closer inspection will reveal that they have simple, undivided leaves unlike the pinnately compound leaf of F. latifolia. A tree species with leaves more closely resembling that of F. latifolia is red elderberry (Sambucus racemosa) which also has pinnately compound leaves, although the leaflets are thin and linear with sharp-toothed margins. In addition, F. latifolia is a more substantial tree. Mountain ashes (Sorbus species) also have pinnately compound leaves, but they are shrubs with alternate sharp-toothed leaflets.

Ecological Value

While fruits of F. latifolia do serve as food for some birds and mammals, its main value lies in its use as a nesting site for birds, including those species that nest within its cavities. Its dense presence throughout some interior valleys of the Pacific Northwest also gives rise to areas known as Oregon Ash woodlands or ash swales, which contain associated species like Salix species, hawthorns (Crataegus species), Alnus species, C. sericea, common snowberry (Symphoricarpos albus), P. capitatus, and slough sedge (Carex obnupta).

Human Value

Old Northwestern folklore maintained that rattlesnakes would not be found anywhere that F. latifolia grew. Today, this tree is the only commercially important ash in the west, providing wood for furniture, flooring, millwork, paneling, boxes and fuel. It also serves as a shade tree along the Pacific Coast.


Guard, Jennifer. Wetland Plants of Oregon and Washington. 1994. Mathews, Daniel. Cascade Olympic Natural History: A Trailside Reference. Raven Editions. 1988. National Audubon Society. Field Guide to North American Trees: Western Region. Alfred A. Knopf, NY. 1980. Plant Life of Washington Territory: Northwestern Pacific Railroad Survey, Botanical Report 1853-1861. Washington Native Plant Society. Vol.5. 1994. Seattle Audubon Society. A Field Guide to the Common Wetland Plants of Western Washington and Northwestern Oregon. Seattle Audubon Society: Seattle, WA. 1997.

This page was created by: Angeline Perla, August 1998

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