Ontario Weeds: Prickly ash

Table of Contents

1. Name
2. Other Names
3. Family
4. General Description
   • Photos and Pictures
5. Stems and Roots
6. Leaves
7. Flowers and Fruit
8. Habitat
9. Similar Species
10. Caution
11. Related Links

Name: Prickly-ash, Xanthoxylum americanum Mill.

Other Names: clavalier d'Amérique, frêne épineux, Zanthoxylum americanum Mill.

Family: Rue Family (Rutaceae)

General Description: Tail shrubs or small trees up to 8m (26ft) high; reproducing by seed and sprouting from spreading underground rhizomes, often forming dense impenetrable stands.

Photos and Pictures

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Stems & Roots: Stems very prickly with pairs of stout, triangular prickles at every node, the needle-sharp tip of each prickle pointing outwards or slightly upwards.

Leaves: Leaves pinnately compound with 2 to 5 pairs of leaflets and 1 terminal leaflet; leaflets narrowly to broadly ovate with a pointed tip, dark green above and light green below, very finely hairy on the underside when young but later becoming smooth, with very small translucent dots due to the presence of oil glands, these resembling pinpricks through the leaf when viewed against the light; leaf margins very shallowly toothed to almost smooth and with a tiny yellowish gland in the base of the notch between the teeth.

Flowers & Fruit: Flowers unisexual, in small umbel-like clusters from the nodes of branches of the previous year and appearing in May before the leaves expand; males and females on different plants; petals 4 or 5, yellowish, very small, 1-2mm (1/25-1/12in.) long; sepals absent; stamens 4 or 5 and longer than the petals in male (pollen-producing) flowers; pistils 3 to 5 in female (seed-producing) flowers, forming small, stalked, spherical or elliptical pods about 5mm (1/5in.) across and splitting across the top to release 2 seeds. Flowers in May; seeds mature in August to September.

Habitat: Prickly-ash occurs in woods and moist meadows in southern and southwestern Ontario.

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Similar Species: It is distinguished from wild and cultivated roses, Rosa spp., [rosier] by its clusters of small yellow flowers on leafless branches in May, and by its pairs of triangular prickles at each node of the stem, rather than irregularly scattered along the stem. Taller shrub and tree forms of Prickly-ash might be confused with Black locust, Robinia spp. [robinier] or Honey-locust, Gleditsia spp. [février] which have compound leaves and may also have pairs of prickles on the stems at the base of each leaf, but it can be distinguished by its small yellow, unisexual flowers that blossom on leafless branches in May, whereas the two locusts have larger, showy, pea-like flowers that blossom after the leaves are out, and by the leaflets of its once-compound leaves having translucent dots and very shallow teeth with tiny yellow glands between the teeth. Its smooth-margined, pinnately compound, alternate leaves resemble those of Poison sumac but its pairs of spines and early yellow flowers are distinctive.

Caution: Because the foliage may be browsed when other forage is scarce and because it has been suspected of having poisoned cattle and sheep in Indiana, it should be viewed with suspicion when present in areas used for pasturing livestock.

Related Links

... on general Weed topics
... on weed identification, order OMAFRA Publication 505: Ontario Weeds
... on weed control, order OMAFRA Publication 75: Guide To Weed Control

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