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common wild yam

Dioscorea villosa

Summary 5

Dioscorea villosa is a species of a twining tuberous vine that is native to and found growing wild in North America.

Barcode data: dioscorea villosa 6

The following is a representative barcode sequence, the centroid of all available sequences for this species.


Comments 7

Like the somewhat similar Greenbriers and Carrion Flowers (Smilax spp.), Wild Yam is a monocot, rather than a dicot. This vine is related to the tropical Yam that is found in grocery stores, but it does not produce edible tubers. Wild Yam can be readily distinguished from similar vines by the palmate venation of its leaves, its racemes or panicles of tiny flowers, and its conspicuous 3-angled seed capsules. In southern Illinois, there is the very similar Dioscorea quaternata (Whorled Wild Yam), which tends to have more whorled leaves than the common Wild Yam that is described here. There is disagreement among authorities regarding the taxonomic status of Whorled Wild Yam

Comments 8

Dioscorea villosa is a highly polymorphic species, exhibiting complex patterns of variation across its geographic range. Characters that have been used previously to delineate taxonomic boundaries within this complex—pubescence, glaucousness, rhizome thickness and shape, length of internodes within the inflorescence, arrangement of proximal leaves, geometry of the stem, and fruit and seed size/shape—fail when individuals from all parts of the range and specimens representing both apical and basal portions of single stems can be examined. At its morphological extremes, D. villosa comprises 1) small vines with tightly congested inflorescences, winged stems, and variously pubescent leaves, occurring in bogs and branch swamps; and 2) robust plants, rigid at the base, the proximal leaves verticillate with large, glaucous blades, from the axils of which arise lax spikes or panicles, inhabiting rocky, upland woods and steep talus slopes. As one ascends from the Atlantic Coastal Plain through the Appalachians, continuing westward to the Great Lakes region, south to the Ozarks, and east to the branch swamps of Georgia, particular morphologies are associated with particular ecological conditions, independent of geography. As well as the morphological extremes, every intermediate condition of leaf, stem, and inflorescence architecture can be found, in all combinations, and variation may be encountered even within individual plants. What sort of genetic structure underlies these patterns of morphological diversity remains an open question. That there is a significant degree of genetic variability within the complex is evident from the chromosome counts thus far reported. Further research is needed to shed light on patterns of gene flow in the complex, and garden studies would be instructive as to the limits of individual plasticity. At present, I can find no natural gaps in the variation between the plants that have been called (albeit ambiguously; see H. H. Bartlett 1910) D. villosa and those called D. quaternata, and therefore I am treating the complex as a single species.

Description 9

This is a herbaceous vine about 5-30' long that branches occasionally. Its slender stems have the capacity to twine around adjacent vegetation and fences, climbing upward and outward. The glabrous stems are light green, pale yellow, reddish green, or dark red. The stems are usually terete; less often, they are bluntly angular or narrowly ridged. Whorled and/or opposite leaves sometimes occur near the base of the vine, otherwise the leaves are alternate. At maturity, individual leaf blades are 2-4" long and 1½-3" across; they are narrowly cordate to cordate, smooth along their margins, and palmately veined (7-11 veins per leaf). The upper blade surface is medium green and glabrous, while the lower surface is pale green and sparsely short-pubescent (less often, glabrous or densely short-pubescent). Very young leaf blades are golden green in appearance. The slender petioles are 1½-6" long, light green to dark red, and glabrous or nearly so; sometimes there are tufts of hair where the petioles join the leaf blades. The leaf blades tend to hang downward from their petioles. Wild Yam is dioecious, producing vines with either all male flowers or all female flowers. On male vines, panicles of numerous male flowers about 4-12" long develop from the leaf axils. Male flowers are arranged in small clusters of 1-3 along the branches of each panicle. Individual male flowers are about 1/8" across, consisting of 6 whitish green or yellowish green tepals and 6 fertile stamens. On female vines, racemes of 5-15 female flowers about 3-9" long develop from the leaf axils. Individual female flowers are about 1/8" across and 1/3" long, consisting of 6 whitish green or yellowish green tepals and a large inferior ovary with 6 infertile stamens. The blooming period occurs during early summer. The female flowers are replaced by 3-celled seed capsules that are ovoid in shape and about 1" long; these capsules are strongly 3-angled and become golden green as they mature. Each cell of the capsule usually contains 2 seeds (less often, only 1). The flattened seeds have broad membranous wings; they are distributed by the wind. The root system is rhizomatous.

Ecology 10

The winged seeds are dispersed by the wind. Small (1933) reported Dioscorea villosa to have numerous fruits, but D. hirticaulis few fruits. Al-Shehbaz and Schubert (1989) reported that the small flowers of dioscoreas may be pollinated by night-flying insects, but that wind pollination may also occur. They stated that in D. quaternata and D. villosa (as well as what Bartlett called D. hirticaulis), the rhizome branching and thickness can be modified by soil texture, habitat, and environment.

Faunal associations 11

There is very little information about floral-faunal relationships for this species. The foliage appears to be avoided as a food source by mammalian herbivores. Dense tangles of this vine can enhance nesting habitat for birds and provide cover for various animals.

Sources and Credits

  1. (c) Jayesh Patil, some rights reserved (CC BY-NC-ND), http://www.flickr.com/photos/31196650@N04/3897183354
  2. (c) Wendell Smith, some rights reserved (CC BY), https://www.flickr.com/photos/wendellsmith/8769833946/
  3. (c) Tom Potterfield, some rights reserved (CC BY-NC-SA), https://www.flickr.com/photos/tgpotterfield/12041525313/
  4. (c) Peter Gorman, some rights reserved (CC BY-NC-SA), https://www.flickr.com/photos/52421717@N00/6980676379/
  5. Adapted by Jonathan (JC) Carpenter from a work by (c) Wikipedia, some rights reserved (CC BY-SA), http://en.wikipedia.org/wiki/Dioscorea_villosa
  6. (c) Barcode of Life Data Systems, some rights reserved (CC BY), http://eol.org/data_objects/30693712
  7. (c) John Hilty, some rights reserved (CC BY-NC), http://eol.org/data_objects/29586494
  8. (c) Missouri Botanical Garden, 4344 Shaw Boulevard, St. Louis, MO, 63110 USA, some rights reserved (CC BY-NC-SA), http://eol.org/data_objects/19829596
  9. (c) John Hilty, some rights reserved (CC BY-NC), http://eol.org/data_objects/29443300
  10. (c) NatureServe, some rights reserved (CC BY-NC), http://eol.org/data_objects/29021992
  11. (c) John Hilty, some rights reserved (CC BY-NC), http://eol.org/data_objects/29443302

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