Common prickly ash is a thicket-forming shrub to 10 feet high, often densely branched above the middle. Occasionally a small tree to 26 feet high. Prickly ash forms thickets by sending up shoots from the underground, creeping stems (rhizomes).
Leaves are alternate, pinnately compound (feather-compound), 4–12 inches long, aromatic, the leaf stalk about 1 inch long; leaflets 5–11; side leaflets without stalks, end leaflet with a short stalk; leaflets get progressively longer from the basal pair, ranging from ¾ to 3 inches long, ⅜–1½ inches wide, egg-shaped or half as broad as long, the tip pointed to blunt, the base rounded, the margin entire or with finely rounded teeth; the upper surface dull deep green, dotted with glands; the lower surface paler, hairy on the veins.
Bark is smooth, gray to dark brown with lighter blotches and scattered, small, light-colored, fairly circular lenticels; bark becomes slightly grooved on old trunks; bark is armed with small, flattened, slightly downward-curving prickles. Wood soft, not strong, light brown.
Twigs are rigid, smooth, dark brown to gray; a pair of prickles at each node, each prickle about ¼ inch long, flat, broad-based, recurved.
Flowers April–May, before the leaves are formed, in small, axillary clusters of 2–10, on twigs of the previous year. Fragrant. Individual flowers are short-stalked. This plant is dioecious, with male (staminate) and female (pistillate) flowers usually on separate plants. Sepals are absent. Petals 4 or 5, broadest at the middle, minute, yellowish green, usually with a fringe of short, crinkly, reddish-brown hairs. Male flowers with 4 or 5 stamens, alternating with the petals; female flowers about ¼ inch long, longer than the male flowers, with 2–5 ovaries per flower.
Fruits June–August, in dense clusters, fruit green to reddish brown, strongly aromatic, about ¼ inch long, globe-shaped, firm, fleshy, surface pitted, splitting down one side; seeds 1 or 2, oval, about ⅛ inch long, finely pitted, glossy black; seed coating oily, aromatic.
Similar species: Prickly ash is the only member of its genus recorded growing naturally in Missouri. A few other shrubs or young trees share some characteristics, however.
- Missouri’s true ash trees (Fraxinus spp.) look rather similar, but their compound leaves are opposite, and they do not have prickles.
- Young specimens of black locust (Robinia pseudoacacia) have spines and pinnately compound leaves, but the leaves typically have 11–19 leaflets, and the leaflets are rounded, lacking pointed tips.
- Honey locust (Gleditsia triacanthos) is common in many of the same habitats as prickly ash. Like prickly ash, it is well-armed, but its spines are much longer, and its spines are often branched. The leaflets on its compound leaves are much smaller.
- Finally, a close relative of prickly ash, Hercules club, or southern prickly ash (Z. clava-herculis), was once reported from southeastern Missouri, but there seems to be no physical evidence to substantiate it. Its native range is to the south of Missouri, from Virginia and Florida to Texas and Oklahoma. Among other differences, its trunk is covered with thick, wartly prickles, it forms its flowers after (not before) the leaves expand, and its leaves have mostly 9–13 (not 5–11) leaflets. You might find this plant growing as an ornamental in a yard or garden.
Habitat and Conservation
Native Americans used the bark and its extracts to treat a variety of ailments. Modern herbalists use preparations made of dried bark and berries to treat several conditions. The common name “toothache tree” comes from the practice of people chewing the twigs or fruits to numb toothache pain. Recent scientific research has shown prickly ash extracts may have promise in formulating antifungal and anticancer drugs.
Prickly ash is occasionally planted as an ornamental tree or shrub. It tolerates drought and poor soils, provides food for birds, which eat the berries, and swallowtail butterfly larvae, which eat the leaves. It is best used as a hedge, screen, or thicket in natural or native woodland plantings.
The genus name, Zanthoxylum, is from Greek words for “yellow” and “wood,” referring to the wood color; americanum is for the shrub’s native home.
Worldwide, there are about 250 species in genus Zanthoxylum. Most of these trees or shrubs occur in subtropical or warm-temperate regions. The fruits of some of the East Asian species are used to make the spice called Sichuan pepper, a component of Chinese five-spice powder. Some species that develop extra-small leaves are popular among bonsai enthusiasts.
Like other members of the Rutaceae (citrus or rue family), prickly ashes have oil glands in the leaves (if you hold a citrus or prickly ash leaf up to the light, you can see these little light-colored dots). The oils in these glands are usually aromatic (crush the leaf and smell it). Wherever rue-family plants occur, they usually have historic medicinal uses.
At least one modern American craft distillery uses prickly ash as one of the botanical ingredients in a bitters it sells; their formulation, they say, is based on an antique home recipe from famed American botanist John Bartram.
Why is “prickly ash” sometimes spelled open, closed, or hyphenated? For a long time, there’s been a movement among some botanists to indicate a plant’s true identity by the way the words in the common name are combined. Because prickly ash is not a true ash (genus Fraxinus, in the olive family), the idea is to hyphenate it (prickly-ash) or spell it closed (pricklyash) to show it’s not really in the same group as green ash, white ash, and so on. Meanwhile, common spellings in most mainstream publications follow the versions printed in dictionaries — which in turn follow the spellings used by a majority of people in their country of publication.
The flowers are a nectar and pollen source for a variety of bees and flies.
Prickly ash leaves are a good Missouri food source for giant swallowtail larvae, which in other regions eat citrus. Spicebush swallowtails also use prickly ash as a food plant.
Several leafhoppers and treehoppers feed on the sap of prickly ash, and at least one of those species seems to have it has its preferred food plant.
The fruit is eaten by birds and small mammals, including red-eyed vireo, northern bobwhite, eastern cottontail, and eastern chipmunk. When the seeds pass undigested through these animals, they may form new colonies far from the parent plant.
Prickly ash, and other perennial plants that grow along streams, rivers, lakes, and ponds, help to stabilize the soil where it might otherwise get washed away in floods.
As one of the early woody colonizers of old fields and pastures, prickly ash plays a role in ecological succession, as those formerly disturbed habitats gradually revert back into woodland.
Thicket-forming shrubs such as prickly ash provide important cover for wildlife, including quail, rabbits, and much more.