Chinese Yam or Cinnamon Vine (Dioscorea oppositifolia, syn. D. batatas)

Description

This deciduous perennial vine grows counterclockwise. The leaves are spear, heart or oval-shaped, and commonly come to a sharp point. They are 1.5 to 3 inches long and up to 1.5 inches wide, and generally grow oppositely along the stem, but may alternate along the upper nodes. A distinctive bronze tint appears in new leaves. The leaf margins, stalks, and stems are purplish. The flowers are small and greenish-white, smell like cinnamon, and bloom in June and July. Small, potato-like structures called bulbils appear in the leaf axils from June through September.

Look-alikes

Bulbils distinguish the Chinese yam from several plants with similarly shaped leaves: native wild yam (Dioscorea villosa), greenbriars (Smilax sp.), morning glories (Ipomoea sp.), and bindweed (Convolvulus arvensis). In addition, the wild yam has clockwise vines and slightly hairy upper leaf surfaces, and greenbriars have blue to purple berries. Some greenbriar species also have thorns.

Impacts & Habitat

In the south-east, Chinese yam is found in riparian habitats, such as the edges of mesic bottomland forests, stream banks and drainage ways, and near roadsides and fencerows. It prefers silt loam soils and intermediate light levels, but its tolerance of full shade enables it to occasionally grow in rich, upland forest interiors. The vines grow quickly over native vegetation, often forming dense, heavy mats that block sunlight, down branches, and kill trees. Reproduction is primarily asexual. Bulbils disperse mostly by floating downstream and can be transported further by animals. They can germinate within two weeks of reaching open soil and will grow in the ground into vertical tubers up to 3 feet long. One vine can produce up to 20 bulbils per year. Seed production has not been documented in the U.S.

Control

Control small, initial populations and those in environmentally sensitive areas by mowing and cutting or grubbing prior to bulbil production. Remove the entire root because any portions remaining may resprout. If continued for many growing seasons, these methods can eradicate the population. Treat large populations with foliar herbicide, such as a 4% solution of glyphosate or triclopyr and a .5-1% non-ionic surfactant. Apply in July to October when the leaves have developed fully but the bulbils have not ripened. When spraying near streams, use herbicides approved for use near water.

Additional Information (Links exit DNR)

Invasive Species Specialist Group
The Global Invasive Species Initiative
Southeast Exotic Pest Plant Council