Zanthoxylum americanum, Prickly ash
A deciduous shrub from northern America with spicy leaves and berries which are used to support the circulation and immune system.
scientific name Zanthoxylum americanum Mill.
family Rutaceae
alternative names Northern prickly ash, common prickly ash, toothache tree
parts used Leaf, bark and fruit
Description
A deciduous shrub with pinnately compound leaves and thorny branches growing up to 4m tall and 4m wide. Prickly ash has short stout spines and pinnate leaves of 5-11 oval leaflets. All parts are pungent and aromatic. Inconspicuous flowers are produced in May-June followed by small black fruits which ripen September-October.
Habitat
The prickly ash is native to central and eastern North America. As an understorey shrub in damp woods and on riverbanks in the wild, it forms dense thickets and can grow in partial shade.
Related plants
A close relative, the southern prickly ash (Z. clava-herculis), has similar actions. Oriental varieties include the Chinese Szechuan pepper (Z. bungeanum) or Japanese pepper tree (Z. piperitum). A study of different species found that different habitats affected the chemical components of volatile and non-volatile oils.1 Higher volatile oil levels in winged prickly ash (Z. armatum) were seen in a warmer and more arid climate.
Prickly ash leaves and unripe berries
Cultivation and harvest
Cultivation
Prickly ash should be planted in well-drained soil that does not dry out. It does well in rocky, calcareous soils. It can grow in sun or on a woodland edge. It does not need frost protection, being hardy to USDA zone 4 (UK zone 3). It is fairly slow growing, at Holt Wood we manage this bush somewhat like a gooseberry bush, each year cutting out crossing branches and aiming for an open goblet kind of shape. For berry production, some advisers say that both male and female plants are needed.
Pests and diseases
Not troubled by insects or diseases, though may need protection from slugs and voles when young.
Propagation
Scarify and soak seed in hot tap water, leaving to stand 24 hours, then cold stratify for four months or sow outside in autumn for spring germination, and keep moist. Germination may be slow, and plants should be kept in a cold frame for the first winter. Cuttings of half-ripe wood may be taken in July/August and rooted in pots in a cold frame. Suckers with roots may also be potted up.
Harvesting
Leaf and bark can be harvested in spring when pruning and berries are harvested when ripe in the autumn. Take care when harvesting as the branches and twigs are thorny.
Therapeutic use
Traditional
Members of the Zanthoxylum family can be found in both temperate and tropical climates, and have long been used for the aromatic spicy foliage, bark and seeds which stimulate secretions. In traditional Chinese medicine the prickly ash treats cold and dampness. In Nigeria the root of Senegal prickly ash (Z. zanthoxyloides) is used as a chewing stick. The description of ‘toothache tree’ in North American usage probably arises from the numbing and tingling sensation experienced when chewing a leaf or seed.
Medicinal actions and uses
Prickly ash actions are carminative, diuretic, diaphoretic, circulatory stimulant, sialogogue, antibacterial, antiviral and antifungal.2 Prickly ash is used mainly in Western herbal medicine for its circulatory stimulant properties, in complaints such as leg cramps and rheumatism.
Clinical applications and research
Some research studies have been carried out, showing anti-inflammatory, antifungal, antiviral and antibacterial effects of various parts of the plant and the distilled essential oil.3 More recent studies suggest that Zanthoxylum species may have a role to play in anti-cancer drug development.4
Sample preparations and dosage
Fresh young leaves and twigs can be used to make a tincture to be given 2-5ml three times daily. The bark can also be used in this way. The bark and berries can be dried and then powdered for capsules. Where increased digestive activity is needed the tincture can be given as 20 drops in hot water, or 1-3g of bark as a decoction three times daily.
Constituents and commerce
Key constituents
Prickly ash contains terpenoid essential oils, flavonoids, isoquinoline alkaloids (lauriflorine and nitidine), alkylamides, coumarins, resins and tannins.
Commerce
Prickly ash is accepted as a natural food flavouring source by the Council of Europe.
Safety
The safety of use of prickly ash in pregnancy has not been established, and it should be avoided due to the alkaloid content. Avoid in conditions with gastrointestinal reflux or ulcers.
Other uses
A culinary spice, the berries are used like pepper.
1 Xiang L, Liu Y, Xie C, et al. (2016) The chemical and genetic characteristics of Szechuan pepper (Zanthoxylum bungeanum and Z. armatum) cultivars and their suitable habitat. Front Plant Sci 7: 467.
2 Busia (2016) vol 2, p437.
3 Bafi-Yeboa N, JT Arnason, J Baker, et al. (2005) Antifungal constituents of Northern prickly ash, Zanthoxylum americanum Mill. Phytomedicine 12: 370-377; Gibbons S, Leimkugel J, Oluwatuyi M, et al. (2003) Activity of Zanthoxylum clava-herculis extracts against multi-drug resistant methicillin-resistant Staphylococcus aureus (MDR-MRSA). Phytother Res 17: 274-275.
4 Zhang M, Wang J, Zhu L, et al. (2017) Zanthoxylum bungeanum Maxim. (Rutaceae): A systematic review of its traditional uses, botany, phytochemistry, pharmacology, pharmacokinetics, and toxicology. Int J Mol Sci 18: E2172.