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Prickly-ash

Zanthoxylum americanum

Common names:
prickly-ash, prickly ash, pricklyash, toothache tree

Content Detail

Prickly-ash is a tall, colony-forming small tree or large shrub reaching 15 to 25 feet tall and wide. Twigs and stems are covered in 1/2 inch prickles making it difficult to use in the landscape. In spite of its common name, it is not  related to ash trees (Fraxinus spp.) of the Olive family. Rarely found in the nursery trade. 

This species is native to the Chicago Region according to Swink and Wilhelm’s Plants of the Chicago Region, with updates made according to current research.

  • Family (English) Rue
  • Family (botanic) Rutaceae
  • Tree or plant type Tree, Shrub
  • Foliage Deciduous (seasonally loses leaves)
  • Native locale Chicago area, Illinois, North America
  • Size range Large shrub (more than 8 feet), Compact tree (10-15 feet), Small tree (15-25 feet)
  • Light exposure Full sun (6 hrs direct light daily), Partial sun / shade (4-6 hrs light daily)
  • Hardiness zones Zone 3, Zone 4, Zone 5 (Northern Illinois), Zone 6 (City of Chicago), Zone 7
  • Soil preference Moist, well-drained soil, Wet soil
  • Tolerances Alkaline soil, clay soil, Dry sites, Occasional drought, Occasional flooding, Wet sites
  • Season of interest late summer
  • Flower color and fragrance Inconspicuous
  • Shape or form Multi-stemmed, Thicket-forming
  • Growth rate Moderate

Native geographic location and habitat:

C-Value: 3. Prickly-ash forms thickets in moist wood edges and areas and along stream banks. In drier sites, it is located on rocky slopes. Native to the upper central United States.

Bark color and texture:

Twigs are brown and smooth, while young shoots are light green and nearly glabrous to pubescent. Pairs of stout prickles up to 1/3 inch long are scattered along the branches, twigs, and shoots. These spines are somewhat flattened and curved. 

Leaf or needle arrangement, size, shape, and texture:

Alternate, dark green, compound leaves reach about 6 to 12 inches long and develop along the twigs and young shoots. Leaflets are finely toothed with a yellow gland between each tooth. Small prickles run along the rachis (stalk) and petiole. Crushed leaves smell like citrus.

Flower arrangement, shape, and size:

Dioecious with male and female flowers on separate plants. Yellowish-green flowers appear before the leaves in clusters along last year’s twigs.

Fruit, cone, nut, and seed descriptions:

The fruit is a red, small, two-valved capsule that  splits down the middle to reveal a shiny black seed.

Plant care:

Prefers full or partial sun and moist to dry soils, but will tolerate different types of soil, including clay-loam and rocky material. This shrub can adapt to light shade, but it may fail to produce flowers and fruit. Difficult to find in the nursery trade.

List of pests, diseases, tolerances and resistance:

No serious pests or diseases. Tolerant of black walnut toxicity.

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