Zanthoxylum americanum Mill.

Common Prickly Ash


CC = 4
CW = 3
MOC = 33

© SRTurner

Family - Rutaceae

Habit - Shrub or small tree, dioecious, colonial from rhizomes.

Stem - To 3 m, usually with a few, ascending branches, the bark relatively smooth, gray to dark brown with lighter blotches and scattered, more or less circular lenticels, occasionally becoming longitudinally fissured on old trunks, armed with small, flattened, slightly downward-curved prickles, these mostly subopposite and stipulelike at the nodes, the twigs gray to dark brown, moderately to densely short-hairy when young, becoming glabrous with age.

Zanthoxylum_americanum_stem.jpg Stem and prickle.

© SRTurner

Leaves - Alternate, compound, short-petiolate. Blades pinnately compound with 5-11 leaflets, these 1-6 cm long, progressively longer from the basal pair, oblong to ovate, angled or short-tapered to a sessile or minutely stalked base, rounded or more commonly angled to a bluntly or sharply pointed tip, the margins entire or minutely scalloped, the upper surface dark green, sparsely to moderately and minutely hairy along the veins, becoming glabrous with age, the undersurface pale green, moderately pubescent with somewhat longer, fine, somewhat tangled hairs, mostly along the veins and near the margins, becoming nearly glabrous with age.

Zanthoxylum_americanum_leaf1.jpg Leaf adaxial.

© SRTurner

Zanthoxylum_americanum_leaf2.jpg Leaf abaxial.

© SRTurner

Inflorescence - Produced before the leaves, small axillary umbellate clusters, the flowers short-stalked, sometimes appearing nearly sessile at flowering, the stalks elongating as the fruits develop.

Flowers - Imperfect. Sepals absent. Petals 4 or 5, 1.5-2.5 mm long, narrowly oblong-obovate, overlapping in bud, yellowish green, with a minutely uneven apical portion and usually a fringe of short, crinkly reddish brown hairs. Stamens in staminate flowers 4 or 5 (absent or reduced to 4 or 5 minute staminodes in pistillate flowers), alternating with the petals, the filaments free, slender, and glabrous, attached outside of a small nectar disc around the ovary base. Ovaries 2-5 per flower, each short-stalked (rudimentary in staminate flowers), glabrous, 1-locular with 2 ovules, rounded or short-tapered at the tip, the styles fused above their bases, the stigma minute, with 2-5 lobes.

Zanthoxylum_americanum_flowers.jpg Pistillate flowers.

© SRTurner

Fruits - 2-5 separate follicles per flower, each 4.5-6.0 mm long, ellipsoid to obovoid, tapered to a short stalk at the base, beaked at the tip, the outer surface leathery, pitted, red to reddish brown, glabrous or minutely hairy. Seeds 1 or 2 per fruit, 4.0-4.5 mm long, obovoid to nearly globose, sometimes (in 2-seeded follicles) somewhat flattened, the outer surface with faint, coarse facets or pits and finely pebbled, black, shiny.

Zanthoxylum_americanum_fruits.jpg Fruits.

© SRTurner

Flowering - April - May

Habitat - Forest openings, bluff tops, savannas, glades, streambanks, pond margins, pastures, fields.

Origin - Native to the U.S.

Lookalikes - None close.

Other info. - This shrub occurs in scattered locations in Missouri. It is largely absent from the Ozark and northwestern regions of the state. Its North American distribution occupies the upper Midwest and extends into New England and Canada. Its ash-like compound leaves and prickly stems are strong hints to the ID.

Photographs taken at Young Conservation Area, Jefferson County, MO, 05-07-2018 (SRTurner).