Ornamental Yam

Dioscorea

* photo taken on July 1 2015 in Columbia, MD

Dioscorea batatas ( Chinese Yam )
Also called Dioscorea polystachya. A perennial vine, reaching up to 17 feet, that is borne from an underground tuber. It is native to upland and bottomland forests in most of central and eastern China, Korea and Japan. It has also naturalized throughout the southeastern and Mid Atlantic U.S. It is grown as a commercial food crop in eastern Asia.
The 3-lobed leaves are up to 3.5 x 4.5 inches in size.
Hardy zones 4 to 8.

Dioscorea nipponica
A perennial vine, reaching up to 17 feet in height, that is borne from an underground tuber. It is native from eastern Russia; south to central & eastern China, Korea and Japan.
The variable leaves, up to 6 x 5 inches in size, range from broadly-cordate to 3 to 7 palmately-lobed.
Hardy zones 2b to 8.

Dioscorea quaternata ( Fourleaf Yam )
A perennial vine, reaching up to 15 feet, that is native to rich woods in eastern North America ( from Nebraska to Minnesota to Wisconsin to Grand Bend, Ontario to Ohio to New Jersey; south to far eastern Texas to northern Florida ). It is also found locally in southern Ontario. A trellis or some kinds of support is required for it to climb.
The cordate, broad-ovate leaves are up to 5 x 4 inches in size. The foliage is bright green at first, turning to dull or glossy deep green. The foliage turns to intense bright yellow during autumn. The leaves are borne in whorls of 4.
The tiny, greenish-yellow flowers are borne on axilliary clusters up to 4 inches in length, during early summer.
Hardy zones 5 to 8 in partial shade on moist, humus-rich, well drained soil.

* photos taken on Oct 21 2014 @ U.S. Botanical Gardens, Washington, DC

* photo taken by Robert H. Mohlenbrock @ USDA SCS. 1991. Southern wetland flora

Dioscorea villosa ( Wild Yam )
A deciduous, tuberous vine, reaching up to 12 feet in height, that is native to moist forests of eastern North America ( from southeast Nebraska to eastern Minnesota to Michigan's Upper Peninsula to southern Ontario to Vermont; south to eastern Texas to far northern Florida ). In the Windsor/Essex County, Ontario regions; it was locally common at Point Pelee, the Lake Erie Islands and the Ohio shoreline during the 1800s. It was also abundant at Detroit during that time.
The alternately-arranged, smooth-edged, broadly-ovate leaves are up to 4 inches in length. The foliage turns to intense bright yellow during autumn.
Hardy zones 4 to 9 in partial to full shade on just about any well drained soil. It is tolerant of floodplain conditions.