Chinese yam (Dioscorea polystachya) is an invasive plant in the yam family (Dioscoreaceae). It rapidly invades natural areas, reduces biodiversity and damages the branches of large trees and shrubs. Manual removal of Chinese yam is possible for small isolated patches; however, multiple herbicide treatments are required for larger infestations. In eastern Asia, Chinese yam is cultivated for its edible tubers and used in traditional Chinese medicine.
Where it's found
In Canada, Chinese yam was found in Point Pelee National Park in southern Ontario in 2019 and is under official control. A few individual plants are also present in cultivation. Chinese yam is native to eastern Asia and has been introduced into North America, where it has spread widely in the central and eastern United States. Chinese yam grows in many habitats including forests, ravines, mountain slopes, riverbanks and disturbed areas.
How to spot it
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Infestation -
Stems with leaves and bulbils -
Leaves -
Small tuber -
Segment of large tuber -
Bulbils
Chinese yam is a perennial climbing vine. It produces cylindrical underground tubers up to 1 m long, from which new stems grow. The hairless, twining stems can be green or purplish-red and grow up to 5 m long. Chinese yam produces broad, heart-shaped leaves that are 3-11 cm long and 3-9 cm wide. Its flowers are small, yellowish and smell similar to cinnamon. Chinese yam commonly produces small, warty, potato-like bulbils in its leaf axils, which fall to the ground and sprout into new plants.
How it spreads
Chinese yam spread throughout the U.S. after intentional introduction as an ornamental garden plant. Within North America, Chinese yam primarily reproduces through above-ground bulbils that are spread by gravity, water and rodents that gather and eat them. New stems can also sprout from discarded pieces of Chinese yam tubers, which can be spread in compost. Because of this, imports of viable Chinese yam tubers for human consumption are prohibited and pose a risk of creating new infestations.
What you can do
- Avoid planting or distributing invasive plants
- Do not dump garden waste in parks, fields, forests or other natural areas
- Declare all plants and related products when returning to Canada
- If you think you've spotted it or see it for sale, report a Chinese yam sighting to the Canadian Food Inspection Agency. We will follow up and determine if further action is needed.
What we are doing
Chinese yam is regulated as a pest in Canada under the Plant Protection Act. Importation and domestic movement of regulated plants and their propagative parts is prohibited.
- RMD-13-04: Consolidated Pest Risk Management Document for pest plants regulated by Canada
- D-12-01: Phytosanitary Requirements to Prevent the Introduction of Plants Regulated as Pests in Canada
More information
- Weed seed: Chinese yam
- Invasive plants field guide
- Learn more about invasive species