Zanthoxylum asiaticum Seeds | Sichuan Pepper
LATIN NAME: Zanthoxylum asiaticum
COMMON NAME: Sichuan Pepper, Asian Prickly Ash
Plant Profile
Orange climber is a thorny liana of Asian and African forests, and it is not a pepper despite the name often printed on the packet. It scrambles up trees to ten metres on stems that are corky, flexible and armed with prickles that point backwards, so that pulling it off a trunk is a painful business. The leaves are divided into three glossy leaflets that smell sharply of citrus when crushed, and the whole plant is a tangle of them in the canopy. Small yellow-green flowers appear in spring, and female plants carry clusters of orange fruits about a centimetre across that taste of orange peel and are eaten by birds and monkeys. This is the plant long known as Toddalia asiatica, moved into Zanthoxylum after molecular work in 2018. Its range runs from Ethiopia and Kenya through India and Southeast Asia to southern China and Taiwan.
Science & Biotechnology
Zanthoxylum asiaticum was the sole member of the genus Toddalia until DNA sequencing showed it nested inside Zanthoxylum, and the transfer was published with two other authors in 2018. The plant is a liana rather than a shrub, and its climbing habit is built on recurved prickles that hook over bark; the stems also produce corky wings that give it some of its local names. Flowers are unisexual by abortion, so a plant may carry male flowers, female flowers or a mixture, and the fruit is orange and aromatic when ripe. The roots are the medicinal part and are rich in coumarins, including compounds with antiplasmodial activity in laboratory tests, which matches the widespread African use of root decoctions against malaria and fever. Extracts have also shown activity against influenza H1N1 in cell culture, though that is a long way from a treatment. Harvest of the slow-growing root from wild stands is a conservation concern across its African range.
Uses & Benefits
In East Africa the root is boiled and taken for malaria, coughs and influenza, and the Maasai use it for the same fevers; it is one of the plants that pharmacological screening keeps returning to. The fruit is edible but thin-fleshed and full of seed, and children eat it in passing. The stems are flexible and thorny enough that the plant makes an effective living fence, and the corky older wood has been used for floats and small handles. In Asia it appears in local medicine for toothache and rheumatism, and the leaves are sometimes used as a wash. For gardeners it is a curiosity rather than a crop: a fast, fierce climber for a strong pergola in a frost-free climate, with citrus-scented foliage and orange fruit in winter. It is not a substitute for Sichuan pepper, and anyone buying it for the kitchen should know that before planting.
Growing from Seed
Take seed from ripe orange fruits, wash off the pulp and sow at once in a gritty mix at 22 to 25 degrees; dried seed germinates erratically and may take three months. Scarifying the hard coat with sandpaper improves the odds. The seedling grows slowly at first and then shoots away once the root is established, so give it a deep pot and a stake early. Plant out in full sun or light shade, in well-drained soil, with a sturdy support, and keep it away from eaves and gutters that it will inevitably reach. Water through the first two dry seasons, then only in prolonged drought. The plant is tender below about minus two, so in cool climates it needs a conservatory or a warm wall. Prune hard in early spring to keep it in bounds, and wear leather gloves: the prickles are hooked and break off in the skin.
Our Take
A thorny orange-fruited climber with citrus-scented leaves and a long medicinal record behind it. It is not a pepper, whatever the label on the packet says.
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