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Trees & Shrubs of the Eloise Butler Wildflower Garden

The oldest public wildflower garden in the United States

Prickly ash flower

Common Name
Prickly-ash (Common Prickly-ash, Northern Prickly Ash, Toothache Tree)


Scientific Name
Zanthoxylum americanum Mill.


Plant Family
Rue (Rutaceae)

Garden Location


Prime Season
Flowers Late April to May; Red fruit in July



Prickly-ash is a native tall shrub, growing to 25 feet in height, with a trunk of up to 6 inches in diameter, but the plant is usually much shorter, growing as a multi-stemmed understory shrub. The wood is a light brown or deep yellow color.

The bark is dark brown with good sized prickles (6mm and up to 13mm long) that are flattened on the sides and somewhat curved. These appear in pairs along the twigs and branches at nodes with the buds.

Twigs are aromatic with a fragrance of lemon peel when crushed. They are light green initially, turning to reddish-brown in the Autumn, then to brown. Buds are are red and woolly and appear above the old leaf scars.

Leaves are alternate, oddly pinnate of usually 5 to 11 ovate leaflets on very short stalks, dark green above and lighter under with light fine hair when young. Fall color is a mellow yellow contrasting with the reddish Autumn color of the new twig.

The inflorescence is a tight cluster of un-stalked flowers appearing on the previous season's wood. They open before the leaves. Most plants are dioecious, that is, with male and female flowers on separate plants.

Flowers are greenish-yellow, about 3 to 3.5mm wide. Male flowers (staminate) have 4 or 5 yellowish-green short erect petals and 4 to 5 stamens, but no calyx. Female flowers (pistillate) have 4 to 5 short erect petals, yellow green also, 2 to 5 pistils and no calyx.

Fruit: Fertile flowers mature to a capsule, (a follicle), turning from green to reddish-brown in the autumn. The capsules split open when mature and the single black oily seed (sometimes two) emerges.


Habitat: Prickly-ash grows in woods and thickets and tolerates some shade and dryer upland soils. It has a suckering habit which will create dense stands, but no insect or disease problems. The flowers and later the red fruit give it landscape interest, but the plant is best kept on the edges of your landscape.

Names: The genus name, Zanthoxylum, comes from xanthos and xylon meaning "yellow wood". The species, americanum, is 'of America'. The author name for the plant classification - "Mill." is for Philip Miller, Scottish botanist (1691-1771) who was chief gardener at the Chelsea Physic Garden and wrote "The Gardener's Dictionary". The name 'toothache tree' is explained below.

Comparisons: When the twigs are bare, the stout prickles may be mistaken for a young Black Locust, Robinia pseudoacacia, except that the Locust has hidden buds, not red exposed buds. After leaf out the flowers and seed capsules are entirely different.

See bottom of page for notes on the Garden's planting history, distribution in Minnesota and North America, lore and other references.

Full plant drawing

Above: A young plant about 6 feet high. Drawing from Britton, N.L., and A. Brown. 1913. An illustrated flora of the northern United States, Canada and the British Possessions. 3 vols. Charles Scribner's Sons, New York.

Below: The pinnate leaf has an odd leaflet number, leaflets on extremely short stalks, largest leaflets near the tip. Nice yellow autumn color contrasts with the twig that has turned reddish.

Prickly ash leaf Prickly ash fall leaf

Below: 1st photo - Spring twig: The thorns of Prickly-ash are paired at the nodes. 2nd photo - The buds are covered with red hair and are quite visible in autumn above the leaf scar.

Prickly ash twig Prickly ash twig

Below: 1st photo - Flowers form on the old wood at each node of the twig, opening before the leaves. 2nd photo - Male flower detail - 4 or 5 petals and no calyx with 4 to 5 stamens. Female flowers have 2 to 5 pistils. 3rd photo - Bark of a main stem. Prickles are evident there also.

Prickly Ash twig Prickly ash flowers Prickly ash trunk

Seed Development

Below: 1st photo - The female flowers beginning to mature into seeds. 2nd photo - Full size green fruit 2 months after flowering.

Prickly Ash new berries Prickly ash green fruit

Below: 1st photo - The shrub with mature seed capsules in Late Summer. 2nd photo - The capsules split open to release a single black seed

Prickly Ash Berry seeds


Notes: Prickly-ash is indigenous to the Garden area. Eloise Butler recorded it on April 29, in her first plant survey of 1907. Many times thereafter she would note planting some new species in the "prickly ash arbor". It was present in the Garden at the time of Martha Crone's 1951 Garden census and on later census lists. The western range of Prickly ash in North America is the Dakotas, Nebraska, Missouri, Oklahoma on a north/south line and from there eastward to the coast excepting only Mississippi in the south and Manitoba in the north. In Minnesota it is found in almost all counties except the far northern tier and the arrowhead. A few scattered exceptions elsewhere. It is on the endangered list in 4 eastern states.

Medicinal uses: There is a fair amount of literature on the historic medicinal use of this plant. The root, bark and berries are the official ingredients, having been listed in the U.S. Pharmacopoeia. Berries and bark have a hot, acrid taste. Bark infusions were used for treating skin problems, swollen joints, back pain, fevers and more. Crushed root was used to treat fever. Bark poultices were used for rheumatism and sharp pains. Infusions of the berries were used to treat hemorrhage, as a cough syrup or to treat other issues. The common name "toothache tree" comes from the use of the bark, beaten or powdered, and packed around an aching tooth. In Minnesota, Densmore (Ref. #5) in her study of the Minnesota Chippewa, reported on two uses: A decoction of the root was used internally for quinsy and swelled throat (also taken as a gargle); second, a decoction of the root was used as a bath to strengthen the legs and feet of a weakly child, especially if the limbs were partly paralyzed. See Hutchins (Ref #12) and Mrs. Grieve (Ref. #7) for more information.

References and site links

References: Plant characteristics are generally from sources 1A, 32, W2, W3, W7 & W8 plus others as specifically applied. Distribution principally from W1, W2 and 28C. Planting history generally from 1, 4 & 4a. Other sources by specific reference. See Reference List for details.