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Wisconsin Plant of the Week

Zanthoxylem americanum Miller

Rutaceae (Rue or Citrus Family)

Common Name:

prickly ash


Prickly ash is a native shrub of deciduous woods that grows to 5 m. It's common at the woods edge or in the interior when land has a history of disturbance such as grazing.  It spreads by suckers from shallow roots, so that a very large patch may be a single plant or clone. In spite of its indicator status, prickly ash is found not only in uplands, but also in moist woods and along streams.

Leaves are pinnately compound similar to those of the ash trees, but prickly ash leaves and branches are alternate. Leaflets are oval with pointed tips, and toothed edges. The edges appear smooth only because the teeth are small and separated by small yellow glands.

Small yellow flowers with 4 or 5 petals bloom in April and May, before the leaves appear.  They form in clusters in the axils of last years twigs.  Prickly ash is dioecious with male and female flowers on separate plants.

The fruits on the female plants are red with a pitted surface and smell like oranges when crushed. Each fruit splits open in the early fall to release a shiny black seed.  The wood is bright yellow and the twigs contain salicylic acid (aspirin), the origin of another common name, "toothache tree."

Prickly ash is easiest to recognize, once it loses its leaves, by the paired broad-based prickles that form at each leaf scar and the red buds of next year's leaves.  Only Black locust (Robinia pseudoacacia) has similar prickles, but the fruit of locust trees are large pea-like pods and the leaflets have round tips.

  • Origin of the name: Zanthoxylum, xanthos, Gr., yellow; xylon, Gr., wood; americanum:  L., from the Americas
  • Range:  s. Que. to e. ND, s. to SC, OK
  • WI Range: Statewide, less common in the north
  • Common associates:  Hawthorne, white ash, buckthorn
  • Wetland Indicator Status: UPL
  • Coefficient of Conservatism: C = 3 (MI);  C = 3 (S&W)
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