Climbing Yams (Dioscorea spp.)
From Bugwoodwiki
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Miller, J.H., E.B, Chambliss, N.J. Loewenstein. 2010. A Field Guide for the Identification of Invasive Plants in Southern Forests. General Technical Report SRS-119. Asheville, NC. United States Department of Agriculture, Forest Service. 126 p.
Contents |
Plant
Herbaceous, high climbing vines to 65 feet (20 m) long, infestations covering shrubs and trees. Twining and sprawling stems with long-petioled heart-shaped leaves. Spreading by dangling potato-like tubers (bulbils) at leaf axils and underground tubers. Monocots.
Stem
Twining and covering vegetation, branching, hairless. Internode cross sections round for air yam to angled for Chinese and water yams. Water yam nodes winged and reddish. All stems dying back in winter leaving some bulbils attached.
Leaves
Alternate (air) or combination of alternate and opposite (Chinese and water). Heart shaped to triangular with elongated tips, thin and hairless, 4 to 8 inches (10 to 20 cm) long and 2 to 6 inches (5 to 15 cm) wide. Long petioled. Basal lobes broadly rounded (air) or often angled (Chinese and water). Margins smooth. Veins curved and converging at tip and base. Dark green with slightly indented curved veins above (quilted appearance) and lighter green beneath. Chinese yam leaves turning bright yellow in fall.
Flowers
May to August. Rare, small, panicles or spikes to 4.5 inches (11 cm) long in axils male and female flowers on separate plants (dioecious). Green to white. Fragrant, with Chinese yam having a cinnamon fragrance (thus the common name cinnamon vine).
Fruit and seeds
June to September (and year round). One to 4 aerial tubers (bulbils) resembling miniature potatoes or yams occur at leaf axils, eventually dropping and sprouting to form new plants. Shape spherical to ovoid (air and Chinese) to oblong (water). Texture smooth with dimples (air) to warty (Chinese) to rough (water). Air yam to 5 inches (12 cm) long, Chinese yam to 1 inch (2.5 cm) long, and water yam to 4 inches (10 cm) long and 1.2 inches (3 cm) wide. Very rarely have capsules and winged seeds, which have questionable viability.
Ecology
Rapid growing and occurring on open sites: water yams in FL, air yams extending from FL to adjacent States, and Chinese yams in all States except FL. All dying back during winter but able to cover small trees in a year, with old vines providing trellises for regrowth. Spread and persist by underground tubers and abundant production of aerial tubers (bulbils), which drop and form new plants and can spread by water. Chinese yam aerial tubers persist only 1 year.
Resembles
Resembles greenbriers (Smilax spp.) with most having thorns and/or green-to-purple berries but no aerial potatoes. Also resemble several native Dioscorea species that do not form dense vine infestations nor have aerial tubers (bulbils): wild yam (D. villosa L.) with hairy upper leaf surfaces; native Florida yam (D. floridana Bartlett); and, only in Florida, nonnative Zanzibar yam (D. sansibarensis Pax.). Chinese yam leaves are a similar shape to the native vine, Carolina coralbead (Cocculus carolinus (L.) DC.), and morning-glory (Ipomea spp.) while their veins are not curved tip to base.
History and use
Introduced from Africa (air) and Asia (Chinese and water) as possible food sources in the 1800s. Ornamentals often spread by unsuspecting gardeners intrigued by the dangling yams. Presently cultivated for medicinal use.
Distribution
Chinese yam found scattered throughout the region, while air and water yam occur along the southern portions of the Gulf Coast States and throughout FL.
Management strategies
- Do not plant. Remove prior plantings, and control sprouts and seedlings.
- Bag and dispose of all aerial yams (bulbils) in a dumpster or burn.
- Treat when new plants are young to prevent seed formation.
- Pull, cut, and treat when fruit are not present.
- Burning and cutting treatments have minimal control due to large underground tubers.
Recommended control procedures
- Thoroughly wet all leaves with one of the following herbicides in water with a surfactant before aerial bulbils form: Garlon 3A or Garlon 4 as a 2-percent solution (8 ounces per 3-gallon mix). Chinese yam bulbils will take up the herbicide; the other species must be collected and destroyed (not composted).
- For safety to surrounding plants, cut climbing plants just above the soil surface and immediately treat the freshly cut stem with Garlon 3A in a 50-percent solution (6 quarts in a 3-gallon mix).
Images
 Photo by James H. Miller, USDA Forest Service, Bugwood.org Air Yam: July |  Photo by James H. Miller, USDA Forest Service, Bugwood.org Chinese Yam: November |  Photo by James H. Miller, USDA Forest Service, Bugwood.org Chinese Yam: July |  Photo by James H. Miller, USDA Forest Service, Bugwood.org Air Yam: July |
 Photo by James H. Miller, USDA Forest Service, Bugwood.org Air Yam: December |  Photo by Fred Nation, Weeks Bay National Estuarine Research Reserve, Bugwood.org Water Yam: August |  Photo by James H. Miller, USDA Forest Service, Bugwood.org Air Yam: December |
