Ox knee is an Asian herb whose root is the source of the Chinese herbal medicine huai niu xi. Its stem joints swell like knees, and its spiny little fruits cling to clothing and fur. The Achyranthes you are likely to find growing wild in the eastern US is its close relative, Japanese chaff flower, an invasive weed along the Ohio River.
Appearance
- Growth form
- A perennial herb 1½–3 ft (50–100 cm) tall, with square stems and swollen joints.
- Leaves
- Paired, oval leaves; thicker and hairier than those of Japanese chaff flower.
- Flowers
- Tiny green flowers without petals, packed in slender spikes at the stem tips.
Look-alikes
Ox knee has thicker, sturdier, hairier stems, thicker leaves, and flowers packed closer together on shorter stalks. Japanese chaff flower is less hairy and grows in partial shade.
Why they get mixed upThe two look almost the same and are sometimes treated as varieties of one species. Japanese chaff flower is the one that escaped in the US: first reported in Kentucky in the 1980s, it was established in nine states of the Ohio River basin by 2014.
Where it lives
- Range
- Native to Asia, including India, Nepal, China, Korea, and Japan.
- Preferred conditions
- In Japan it grows on sunny roadsides, vacant lots, and gardens, more than its shade-loving relative, Japanese chaff flower.
Life cycle
- Seed dispersal
- The small around each fruit harden into spines, so the fruits hitch rides on animals and clothing.
Cautions
- Cautions
- In China the plant was historically used to cause abortion, and East Asian herbal medicine avoids it in pregnancy.
Conservation
- IUCN Red List
- NENot EvaluatedNot yet assessed
Culture and stories
- Culture and stories
- The seeds have been eaten in place of grain during famine years.
More species to explore
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