Dioscorea villosa - L.
Yellow Yam
Other English Common Names: Wild Yam
Other Common Names: wild yam
Taxonomic Status: Accepted
Related ITIS Name(s): Dioscorea villosa L. (TSN 43367)
French Common Names: dioscorée velue, igname velue
Unique Identifier: ELEMENT_GLOBAL.2.153733
Element Code: PMDIO010C0
Informal Taxonomy: Plants, Vascular - Flowering Plants - Other flowering plants
 
Kingdom Phylum Class Order Family Genus
Plantae Anthophyta Monocotyledoneae Liliales Dioscoreaceae Dioscorea
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Concept Reference
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Concept Reference: Kartesz, J.T. 1994. A synonymized checklist of the vascular flora of the United States, Canada, and Greenland. 2nd edition. 2 vols. Timber Press, Portland, OR.
Concept Reference Code: B94KAR01HQUS
Name Used in Concept Reference: Dioscorea villosa
Taxonomic Comments: Common names: wild yam (Kartesz 1999), Atlantic yam, common wild yam, wild yam-root, yellow yam; colic root, rheumatism root.

The similar Dioscorea quaternata has frequently been confused or combined with Dioscorea villosa, but it is "very distinct" and readily distinguishable by its smoothly round and wingless stems, and whorled lower leaves (3-9 at a node). The inflorescences and flowers of Dioscorea floridana differ in several substantial ways from those of both of these species (see Al-Shehbaz and Schubert 1989).

Collectors of wild yams in the U.S. east and south for the medicinal plant trade may obtain several biological (taxonomic) entities which get named "Dioscorea villosa". This is especially so because the taxonomy of the continental U.S. dioscoreas, which probably involves three native species, has been quite confused in botanical literature and is still unsettled (Al-Shehbaz and Schubert 1989; Ward 1977; Weakley 1997; Kartesz 1999). In addition, four exotic species have naturalized to varying extents; one or two of the aliens can also be found in many states of this region, and in Florida three of them occur (Kartesz 1999; Al-Shehbaz and Schubert 1989), but the exotic species are distinctively different and unlikely to be confounded morphologically with the native species. However, in browsing information on the Web via Internet searches, the name Dioscorea villosa is sometimes used very loosely and sometimes more or less as a marketing label, even for wild yams from Mexico and/or Central America.

Kartesz (1999) recognizes three native species occurring in the U.S./Canada region: Dioscorea floridana Bartlett, D. quaternata J.F. Gmelin and D. villosa L.; he placed D. hirticaulis Bartlett [D. villosa var. hirticaulis (Bartlett) Ahles] (hairy wild yam, hairy-stemmed wild yam) in synonymy under D. villosa. This treatment agrees somewhat with Al-Shehbaz and Schubert (1989), which may be the most penetrating analysis thus far, although they did not thoroughly discuss the species as found beyond the Southeast. Other authors of floras and checklists have interpreted these four taxa variously, placing one or more within D. villosa either in synonymy or as distinct taxonomic entities (usually variety); there are details in Al-Shehbaz and Schubert (1989).

Braun (1967) commented on the variable morphology of D. villosa and D. quaternata (considering D. glauca Muhl. ex Bartlett a synonym of the latter). Gleason (1952) noted that plants with glabrous leaves have been distinguished as D. villosa fo. glabrifolia (Bartlett) Fern. [D. villosa var. glabrifolia (Bartlett) Blake], which was recognized by Steyermark (1963) (but not Yatskievych 1999). Kartesz (1999) places this taxon (as a variety attributed to Fernald rather than Blake) in the synonymy of D. quaternata, in agreement with Al-Shehbaz and Schubert (1989); however Yatskievych (1999) treats it as a synonym of D. villosa. Ward (1977) reported (which Weakley [1997] notes) that Shu-Fun Au in an unfinished (and unpublished) study had tentatively recognized D. hirticaulis and D. villosa (as well as D. floridana), but that "all" other entities were considered synonyms of D. villosa.

Al-Shehbaz and Schubert (1989) emphasize that Dioscorea villosa and D. quaternata are both highly variable in stem and leaf pubescence (with a spectrum of leaf variability within some populations and leaf pubescence and glaucesence not of taxonomic value), and that rhizome branching, thickness and surface configuration can be modified by environmental factors. Gleason (1952) had accepted Dioscorea hirticaulis (as occurring on wet alluvial soil from southern Virginia to southern Indiana and southward), although stating it was little known and possibly not deserving of specific rank (Al-Shehbaz and Schubert [1989] believe the Indiana plants are D. quaternata). Fernald (1970) recognized D. hirticaulis, but with a more restricted range of southern New Jersey to Georgia. Gleason and Cronquist (1991) note that some plants of the Coastal Plain with the stem hairy and relatively few-flowered inflorescences have been segregated as D. villosa var. hirticaulis. Radford et al. (1968) accepted this variety; so has Weakley (1997), but with commentary regarding conflicting information and the need for study. Al-Shehbaz and Schubert (1989) furthermore report that the type specimen of D. villosa is morphologically what has been called D. hirticaulis!

A scenario or sketch to understand the taxonomic results of the study by Al-Shehbaz and Schubert (1989) is as follows. In considering the Dioscorea villosa complex (particularly D. hirticaulis, D. quaternata, D. villosa), Al-Shehbaz and Schubert (1989) decided that two usually recognized species were not clearly different and could not be maintained, and moreover that they should be simply combined into one variable species, rather than being considered one species with two subspecies, varieties, or forms. They also decided that there were two good biological entities in the complex, that they were very distinct, and that they should be recognized as species. One is a regional species, the other a very widespread species.

The names for the two good species might have been D. hirticaulis and D. villosa, with D. quaternata just as a synonym of D. villosa, since they were not recognizing for example a D. villosa subsp. villosa and a D. villosa subsp. quaternata (J.F. Gmelin) Knuth. However, it was determined that the type specimen (the standard for the name) D. villosa was a plant of the regional species, not the widespread species. Consequently, they call the Atlantic Coastal Plain species D. villosa (synonym D. hirticaulis). The widespread and quite variable species is therefore called D. quaternata. Bruce MacBryde, Jan. 2000
Conservation Status
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NatureServe Status

Global Status: G4G5
Global Status Last Reviewed: 31Jan2000
Global Status Last Changed: 07Feb2000
Rounded Global Status: G4 - Apparently Secure
Reasons: Dioscorea villosa seems to be inadequately understood taxonomically, and the existing knowledge seems to be too little known (note Ward 1977, Weakley 1997, Yatskievych 1999); this biological entity may be a regional Coastal Plain species as Al-Shehbaz and Schubert (1989) interpret it, rather than the much more widespread taxon Kartesz (1999) has mapped. In addition, perhaps it is more restricted to wetland habitats, which themselves have undergone considerable loss and continue to be threatened, and the species (and/or wild yam under the name Dioscorea villosa) is of considerable collecting interest for the medicinal trade. Dioscorea villosa var. hirticaulis is not taxonomically recognized by Kartesz (1999), but it is recognized for example by Weakley (1997), whereas Al-Shehbaz and Schubert (1989) recognize the morphology of what had been considered D. hirticaulis under the name D. villosa but do not recognize two entities within either D. villosa or D. quaternata.
Nation: United States
National Status: N4N5
Nation: Canada
National Status: N4 (04Oct2017)

U.S. & Canada State/Province Status
Due to latency between updates made in state, provincial or other NatureServe Network databases and when they appear on NatureServe Explorer, for state or provincial information you may wish to contact the data steward in your jurisdiction to obtain the most current data. Please refer to our Distribution Data Sources to find contact information for your jurisdiction.
United States Alabama (SNR), Arkansas (SNR), Connecticut (SNR), Delaware (S5), District of Columbia (S5), Florida (SNR), Georgia (S5), Illinois (S5), Indiana (SNR), Iowa (S4), Kansas (S2), Kentucky (S5), Louisiana (SNR), Maryland (SNR), Massachusetts (SNR), Michigan (SNR), Minnesota (SNR), Mississippi (SNR), Missouri (SNR), Nebraska (S1), New Jersey (SNR), New York (S5), North Carolina (S5), Ohio (SNR), Oklahoma (SNR), Pennsylvania (SNR), Rhode Island (S2), South Carolina (SNR), Tennessee (SNR), Texas (SNR), Virginia (S4S5), West Virginia (S5), Wisconsin (SNR)
Canada Ontario (S4)

Other Statuses

NatureServe Global Conservation Status Factors

Range Extent Comments: Al-Shehbaz and Schubert (1989) state that Dioscorea quaternata is the most variable and widespread of the three native species, occurring primarily east of the 95th meridian (e.g. western Missouri border) and between 27?-45?N latitudes (e.g. central Florida to northern New York). Some of the inland dioscoreas have usually been treated as D. villosa, but they seem to consider all those plants to be D. quaternata. They state that Dioscorea villosa (based on the type of what had been considered D. hirticaulis) ranges from Rhode Island and southwestern Massachusetts southward along the Coastal Plain into northern Florida; they consider it disjunct in Kentucky, and probably introduced. Weakley (1997) tends to accept the distribution given in Al-Shehbaz and Schubert (1989), stating that D. villosa var. villosa is primarily in the Coastal Plain. The range of D. floridana they indicate as in certain counties of South Carolina, Georgia and Florida.

However, although Kartesz (1999) seems to agree with the taxonomic view of Al-Shehbaz and Schubert (1989) in recognizing the same three species (and no varieties or subspecies), he does not accept their geographic concepts for the two more extensively distributed species, but indicates that Dioscorea villosa also occurs inland beyond the Coastal Plain with nearly the range of D. quaternata, as most floras and checklists have indicated (he also notes voucher specimens in various states' herbaria, but it is not clear whether these have been verified by him). The recent flora by Yatskievych (1999) similarly has the more traditional widespread treatment of both species. Morton and Venn (1990) point out that reports of Dioscorea villosa in Canada (Ontario) are erroneous according to Al-Shehbaz and Schubert (1989); the only species there is D. quaternata, with which Kartesz (1999) agrees.

Whereas Kartesz (1999) reports Dioscorea villosa in Puerto Rico (citing Britton and Wilson's flora), Liogier and Martorell (1982) treat that name under the introduced D. cayenensis Lam. and do nototherwise address D. villosa. Kartesz (1999) reports that both occur there.

Number of Occurrences:  
Number of Occurrences Comments: Al-Shehbaz and Schubert (1989) reported Dioscorea villosa to be common in the Carolinas and Virginia, with only old historic records for New Jersey and New York. They considered Dioscorea quaternata very rare in the peripheral states of its range in New Jersey, New York, Wisconsin, Minnesota, Iowa, Kansas, Oklahoma and Texas, but quite common in the other states within its extensive range; it was considered sporadic in southern Ontario (Canada). Weakley (1997) states that the latter species is more northern and montane than D. villosa, and is centered on and most abundant in the Appalachians.

Weakley (1997) states that Dioscorea villosa var. villosa is uncommon in moist forest and woodlands of the Carolinas and Virginia, and that D. villosa var. hirticaulis is rare on mesic soils of sandhill-pocosin ecotones and in mesic forest. He considers D. quaternata common in moist forests. The following three accounts from floras may be mixtures, with some plants of Dioscorea quaternata as understood by Al-Shehbaz and Schubert (1989). Radford et al. (1968) stated that D. villosa var. villosa was common in woodlands throughout the Carolinas, and D. villosa var. hirticaulis widely scattered and infrequent on the Coastal Plain in swamp forests and alluvial woods. Barry (1980) considered D. villosa common or frequent in South Carolina in the floodplain of piedmont forests and in upland forests. According to Hough (1983), in New Jersey D. villosa was statewide and frequent, but decreasing on the outer Coastal Plain, and D. hirticaulis local and rare.

The following accounts which their authors consider to be about Dioscorea villosa may instead refer entirely to plants of a variable Dioscorea quaternata as understood by Al-Shehbaz and Schubert (1989), but not Kartesz (1999) as he considers that both species have inland distributions. Dioscorea villosa was stated by Core (1978) to be common throughout West Virginia in moist woods and thickets, occurring in every county (he considered D. quaternata much less widespread, occurring in thickets). Braun (1967) said that Dioscorea villosa was found almost throughout Ohio, being widespread and common (she considered D. quaternata to occur only in southern Ohio). Steyermark (1963) reported Dioscorea villosa fo. villosa to occur throughout Missouri, probably in every county, but D. villosa fo. glabrifolia (which Al-Shehbaz and Schubert [1989] consider a synonym of D. quaternata) to be scattered over the state throughout the range of the more common form (he considered D. quaternata to occur only through the southeastern Ozark region). Yatskievych (1999), publishing well after Al-Shehbaz and Schubert (1989), is similar to Steyermark (1963) in recognizing both species in Missouri and considering Dioscorea villosa scattered throughout the state (now with D. villosa fo. glabrifolia as a synonym, but of D. villosa rather than D. quaternata), and D. quaternata scattered only through the southeastern Ozark region.

Overall Threat Impact Comments: There is evidence, obtained from reliable sources, of wild-collection for the plant trade.

As with the taxonomy and the geography, the Dioscorea species used in some medicinal studies and the market are frequently not clear in the information reviewed. The stimulus in recent decades for the medicinal trade in the native wild yam(s), dioscoreas or Dioscorea villosa relates to their ongoing perceived value in having hormonal or hormonal-like properties in the rootstocks, either by having the particular substance(s) desired or precursor molecules that the body can convert into desirable substance(s) (e.g. Lininger 1999). Tierra (1988) highlighted hormonal precursors of progesterone and cortisone, indicating the plant's usage to treat various kinds of discomfort and pain such as colic, menstrual cramps and neuralgia. Mowrey (1986) provided some details regarding biochemical pathways (from glycoside saponins) and the usage (in mixtures with other plants) of wild yam root as a female tonic and for liver disorders. Lininger (1999) notes some other medicinal uses, but also reports that contrary to popular claims, wild yam roots do not contain nor does the human body physiologically convert yam substances into progesterone or DHEA, stating that conversion of the precursors requires an industrial process. Glickman (1999) recommends the use of Dioscorea villosa instead of DHEA, emphasizing that the supplements taken need to be concentrated and of this species, not other species. Some of this discussion relates to whether the plant precursors themselves might be medicinally beneficial. A skin cream is also marketed.

Prescott-Allen and Prescott-Allen (1982) stated that hormones are the second largest category of Western drugs, and most are steroids made by partial synthesis from natural products. Until 1976 the most important source was diosgenin, which was obtained from wild as well as cultivated plants of several species of Dioscorea native in Mexico and Guatemala or in the Himalayas (Huxley 1984; Mowrey 1986; Simpson and Ogorzaly 1986; Foster and Duke 1990) - but not from the U.S. species. (For example, in 1974 the price of the raw material was US$ 27.68/kg, with Mexico providing 600 tons from D. mexicana [and/or D. floribunda, D. composita], at more than US$ 16.6 million.) However, in 1974 or 1975 Mexico increased the price sharply, stimulating the more active seeking of alternative sources (Myers 1983); by 1976 Mexican diosgenin had been displaced by stigmasterol from soybeans (Glycine max). Most oral contraceptives, one of the biggest products derived from diosgenin, are considered to now be manufactured by total synthesis. Also, the cells of a Mexican species are cultured, a quicker and less costly technique to obtain the diosgenin (Myers 1983).

India and China [at least for some time] found it cost-effective to continue to use diosgenin from their wild yams as the precursor for oral contraceptives and other steroids (e.g. cortisone). Huxley (1984) said the Himalayan Dioscorea deltoidea has been so heavily overcollected that the genetically higher-yielding plants (which produced large tubers) are gone, with the diosgenin content of the plants remaining in one studied area being reduced from over 6% to below 1%.

The part of the plant collected for medicinal usage is the rootstocks (rhizomes). Fresh plants may be toxic (Foster and Duke 1990).

Michael McGuffin (pers. comm.) said that the American Herbal Products Association (AHPA) fairly recently surveyed its members regarding their trade in various species. He stated that their figures should be considered preliminary, and in general might include some double counting (if one company supplied another), resulting in over-reporting by as much as twice the actual amount. Thus a maximum total of 20,000-25,000 pounds per year of dried roots of "wild yam" ("Dioscorea villosa" and presumably other Dioscorea species, perhaps including material from Mexico and Central America) may have been supplied in 1990, 1991 and 1992 by those members who responded, or the actual total might be only half the above (McGuffin pers. comm.). He noted that this amount might include yam material of wild and cultivated origins. The AHPA has included "wild yam (Dioscorea spp.)" in a more definitive planned tonnage survey for the 1999 season (McGuffin pers. comm.).

The native dioscoreas are somewhat associated with wetland habitats, which frequently are under threat.

Short-term Trend Comments: May be declining. According to Hough (1983), in New Jersey Dioscorea villosa was statewide and frequent, but decreasing on the outer Coastal Plain, and D. hirticaulis local in the southeast and endangered. The New Jersey Heritage Program considers D. villosa var. hirticaulis to be S2. Kartesz (1999) reports D. villosa itself to be rare in the state (noting a voucher specimen and a personal communication from Janice Meyer), and considers D. hirticaulis to be a synonym of it.

Ward (1977) stated that Dioscorea glauca had been considered a montane species with greater medicinal value, but the "discrimination slowly eroded during the latter half of the 19th century by depletion of the stock ... and adulteration by rhizomes of other species"; it is now considered a synonym of D. quaternata.

The herbal industry organization United Plant Savers maintains "Wild Yam (Dioscorea villosa, D. spp.)" on its "At Risk List" (UpS 1999). This is so even though after the list was first published [about 1997], some commenters from the east and south reported local abundance of "Wild Yam" (see UpS 1998). Veninga and Zaricor (1976), in commenting on the lack of cultivation of D. villosa as a special crop, noted that a further increase in supply of the root would be beneficial.

Other NatureServe Conservation Status Information

Distribution
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Global Range: Al-Shehbaz and Schubert (1989) state that Dioscorea quaternata is the most variable and widespread of the three native species, occurring primarily east of the 95th meridian (e.g. western Missouri border) and between 27?-45?N latitudes (e.g. central Florida to northern New York). Some of the inland dioscoreas have usually been treated as D. villosa, but they seem to consider all those plants to be D. quaternata. They state that Dioscorea villosa (based on the type of what had been considered D. hirticaulis) ranges from Rhode Island and southwestern Massachusetts southward along the Coastal Plain into northern Florida; they consider it disjunct in Kentucky, and probably introduced. Weakley (1997) tends to accept the distribution given in Al-Shehbaz and Schubert (1989), stating that D. villosa var. villosa is primarily in the Coastal Plain. The range of D. floridana they indicate as in certain counties of South Carolina, Georgia and Florida.

However, although Kartesz (1999) seems to agree with the taxonomic view of Al-Shehbaz and Schubert (1989) in recognizing the same three species (and no varieties or subspecies), he does not accept their geographic concepts for the two more extensively distributed species, but indicates that Dioscorea villosa also occurs inland beyond the Coastal Plain with nearly the range of D. quaternata, as most floras and checklists have indicated (he also notes voucher specimens in various states' herbaria, but it is not clear whether these have been verified by him). The recent flora by Yatskievych (1999) similarly has the more traditional widespread treatment of both species. Morton and Venn (1990) point out that reports of Dioscorea villosa in Canada (Ontario) are erroneous according to Al-Shehbaz and Schubert (1989); the only species there is D. quaternata, with which Kartesz (1999) agrees.

Whereas Kartesz (1999) reports Dioscorea villosa in Puerto Rico (citing Britton and Wilson's flora), Liogier and Martorell (1982) treat that name under the introduced D. cayenensis Lam. and do nototherwise address D. villosa. Kartesz (1999) reports that both occur there.

U.S. States and Canadian Provinces

Due to latency between updates made in state, provincial or other NatureServe Network databases and when they appear on NatureServe Explorer, for state or provincial information you may wish to contact the data steward in your jurisdiction to obtain the most current data. Please refer to our Distribution Data Sources to find contact information for your jurisdiction.
Color legend for Distribution Map

U.S. & Canada State/Province Distribution
United States AL, AR, CT, DC, DE, FL, GA, IA, IL, IN, KS, KY, LA, MA, MD, MI, MN, MO, MS, NC, NE, NJ, NY, OH, OK, PA, RI, SC, TN, TX, VA, WI, WV
Canada ON

Range Map
No map available.


U.S. Distribution by County Help
State County Name (FIPS Code)
MA Hampden (25013)
NE Richardson (31147)
* Extirpated/possibly extirpated
U.S. Distribution by Watershed Help
Watershed Region Help Watershed Name (Watershed Code)
01 Westfield (01080206)+
10 Tarkio-Wolf (10240005)+, Big Nemaha (10240008)+
+ Natural heritage record(s) exist for this watershed
* Extirpated/possibly extirpated
Ecology & Life History
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Basic Description: Male and female (dioecious) counterclockwise-twining vines from slender perennial rootstocks (rhizomes). The herbaceous annual stems are up to 5 m long, with 8-14 angles and lengthwise ribs or narrow wings (well illustrated in Al-Shehbaz and Schubert 1989); the leaves are alternate even on the lower stem, and are heart-shaped and prominently veined. The rather large seeds are flat and broadly winged.
Ecology Comments: 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.
Habitat Comments: Several of the native dioscoreas recognized by Kartesz (1999) may occur in the same general region or area (see section on global range), although the habitats of the three species perhaps are somewhat distinct.

Al-Shehbaz and Schubert (1989) state that in Virginia and the Carolinas (where they considered it to be common), Dioscorea villosa grows in bogs, swamps and peaty depressions. They report Dioscorea quaternata to occur in moist, rich or rocky woods and thickets, on limestone or talus slopes, along roadsides and railroads tracks and the borders of swamps, marshes and ponds, and in creek bottoms. They state that Dioscorea floridana occurs in moist thickets and swamps, as well as moist to dry woods and hammocks.

The following three statements which their authors consider to be about Dioscorea villosa, are probably in part or perhaps mainly about Dioscorea quaternata as understood by Al-Shehbaz and Schubert (1989). Radford et al. (1968) reported Dioscorea villosa var. villosa to occur in woodlands throughout the Carolinas. In South Carolina's piedmont in floodplain forest, Barry (1980) stated that the vines usually found are very common species such as Dioscorea villosa. Harshberger (1911) noted several similar associations near streams that included the species in Delaware and southeastern Pennsylvania (though Al-Shehbaz and Schubert [1989] mentioned they had not seen specimens from Delaware).

The following three statements, although also about Dioscorea villosa according to their authors, may actually be attributable instead just to Dioscorea quaternata as understood by Al-Shehbaz and Schubert (1989). Harshberger (1911) reported that on the piedmont in middle Georgia, Dioscorea villosa occurred in rich shady primeval forest on north-facing hills. In South Carolina in the Blueridge Province, Barry (1980) stated that in upland oak and ridgetop forest there is "a virtual preponderance" of Dioscorea villosa along with several other species. Core (1966) noted the species to be frequent in West Virginia in the rich alluvial soil at the edge of floodplain forest, among or in front of shrubs lining streambanks.

Economic Attributes
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Economically Important Genus: Y
Commercial Importance: Indigenous crop, Minor cash crop
Economic Uses: MEDICINE/DRUG
Production Method: Wild-harvested
Economic Comments: Prices for this species were found as follows:

U.S., internet: $15.00/lb dry root (either cut and sifted or powder)

Management Summary Not yet assessed
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Population/Occurrence Delineation Not yet assessed
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Population/Occurrence Viability
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U.S. Invasive Species Impact Rank (I-Rank) Not yet assessed
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Authors/Contributors
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NatureServe Conservation Status Factors Edition Date: 31Jan2000
NatureServe Conservation Status Factors Author: Bruce MacBryde (2000)

Botanical data developed by NatureServe and its network of natural heritage programs (see Local Programs), The North Carolina Botanical Garden, and other contributors and cooperators (see Sources).

References
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  • Al-Shehbaz, I.A., and B.G. Schubert. 1989. The Dioscoreaceae in the southeastern United States. J. Arnold Arboretum 70: 57-95.

  • Barry, J.M. 1980. Natural vegetation of South Carolina. University of South Carolina Press, Columbia.

  • Bartlett, H.H. 1910. The source of the drug Dioscorea, with a consideration of the Dioscoreae found in the United States. U.S. Bureau Plant Industry Bulletin 189: 1-29.

  • Braun, L.E. 1967. The Monocotyledoneae: cat-tails to orchids. Vol. One. Ohio State Univ. Press, Columbus, Ohio. 464 pp.

  • Core, E. L. 1966. Vegetation of West Virginia. McClain Printing Co., Parsons, West Virginia. 217 pp.

  • Core, E.L. 1978. Flora of West Virginia. 2nd edition. Seneca Books, Grantsville, West Virginia.

  • Deam, C. C. 1940. Flora of Indiana. Division of Forestry, Dept. of Conservation, Indianapolis, Indiana. 1236 pp.

  • Fernald, M.L. 1970. Gray's manual of botany. 8th edition. 1970 printing with corrections by R.C. Rollins [of 1950 8th edition]. D. Van Nostrand Company, New York.

  • Foster, S., and J. Duke. 1990. A Field Guide to Medicinal Plants- Eastern and Central North America. Peterson Field Guides Series. Houghton Mifflin Company, Boston. 366 pp.

  • Gleason, H.A. 1952. The new Britton and Brown illustrated flora of the northeastern United States and adjacent Canada. 3 volumes. Hafner Press, New York. 1732 pp.

  • Gleason, H.A., and A. Cronquist. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. New York Botanical Garden, Bronx, New York. 910 pp.

  • Glickman, J., Jr. 1999. Health science report--Topics: Dioscorea. Online. Available: http://www.alotek.com/topics/dioscorea99.asp. (Accessed 1999 November 3.)

  • Harshberger, J.W. 1911. Phytogeographic survey of North America. Reprinted 1958 ("2nd edition"). H.R. Engelmann (J. Cramer), Weinheim/Bergstr., Germany and Hafner Publishing Company, New York. 790 pp.

  • Hough, M.Y. 1983. New Jersey wild plants. Harmony Press, Harmony, NJ. 414 pp.

  • Huxley, A. 1984. Green inheritance: The World Wildlife Fund book of plants. Collins Sons & Company. Harvill, London.

  • Johnson, T. 1999. CRC Ethnobotany Desk Reference. Online. Available: http://www.herbweb.com/herbage. Accessed 1999, November.

  • Kartesz, J.T. 1994. A synonymized checklist of the vascular flora of the United States, Canada, and Greenland. 2nd edition. 2 vols. Timber Press, Portland, OR.

  • Kartesz, J.T. 1996. Species distribution data at state and province level for vascular plant taxa of the United States, Canada, and Greenland (accepted records), from unpublished data files at the North Carolina Botanical Garden, December, 1996.

  • Kartesz, J.T. 1999. A synonymized checklist and atlas with biological attributes for the vascular flora of the United States, Canada, and Greenland. First edition. In: Kartesz, J.T., and C.A. Meacham. Synthesis of the North American Flora, Version 1.0. North Carolina Botanical Garden, Chapel Hill, N.C.

  • Liogier, H.A., and L.F. Martorell. 1982. Flora of Puerto Rico and adjacent islands: A systematic synopsis. Editorial de la Universidad de Puerto Rico, Rio Piedras. 342 pp.

  • Mabberley, D.J. 1998. The plant-book. 2nd edition. 1998 printing with corrections [of 1997 2nd edition]. Cambridge University Press, Cambridge.

  • Morton, J.K., and J.M. Venn. 1990. A checklist of the flora of Ontario vascular plants. University of Waterloo, Waterloo, Canada. 218 pp.

  • Mowrey, D.B. 1986. The scientific validation of herbal medicine. Cormorant Books, Dunvegan, Ontario, Canada. 316 pp.

  • Myers, N. 1983. A wealth of wild species: Storehouse for human welfare. Westview Press, Boulder, Colorado.

  • NCPMH. 2000. National Center for the Preservation of Medicinal Herbs. Online. Available: http://www.ncpmh.org/phases.html & /wilyam.html. Accessed 2000, January.

  • Prescott-Allen, R., and C. Prescott-Allen. 1982. What's wildlife worth? Economic contributions of wild plants and animals to developing countries. Earthscan, London, England.

  • Radford, A.E., H.E. Ahles, and C.R. Bell. 1968. Manual of the vascular flora of the Carolinas. Univ. North Carolina Press, Chapel Hill, NC. 1183 pp.

  • Simpson, B. B., and M. C. Ogorzaly. 1986. Economic botany. Plants in our world. McGraw Hill Book Co., New York. 640 pp.

  • Small, J.K. 1933. Manual of the southeastern flora. Two volumes. Hafner Publishing Company, New York.

  • Stewart, K. 1999. Where have all the flowers gone? Online. Available: http://www.nfm-online.com/nfm_backs/Feb_99/echinacea.html. Accessed 2000, January.

  • Steyermark, J.A. 1963. Flora of Missouri. Iowa State Univ. Press, Ames. 1728 pp.

  • Swink, F., and G. Wilhelm. 1994. Plants of the Chicago Region. Morton Arboretum. Lisle, Illinois.

  • Tierra, M. 1988. Planetary herbology. Lotus Press, Santa Fe, New Mexico.

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  • Yatskievych, G. 1999. Steyermark's Flora of Missouri, Volume 1. Revised edition. Missouri Department of Conservation, Jefferson City and Missouri Botanical Garden Press, St. Louis.

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