Assessing the genetic diversity, distribution, and population status

of American ginseng (Panax quinquefolius L.) in the eastern U.S.John Young, Tim King, and David SmithUSGS Leetown Science Center, 11649 Leetown Road, Kearneysville, West Virginia, USA 25430 jyoung@usgs.gov

Introduction:

American ginseng (Panax quinquefolius L.) is a perennial herb native to North America that is harvested for the

medicinal qualities of its fleshy taproot, particularly for export to Asian markets to augment demand for Asian

ginseng (Panax ginseng). Harvest and export of ginseng roots to Asia has since the early 1800’s been a source of

supplementary income for people living in the Appalachian Mountains, but recent increases in the market value of

American ginseng roots have intensified legal (and illegal) harvest pressure. American ginseng was listed in

Appendix II of the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES) in

1975. Under CITES, the U.S. Fish and Wildlife Service (USFWS) must determine whether the export of American

ginseng will be detrimental to the survival of the species, and whether wild-harvest is sustainable.

In natural settings, American ginseng is a self-compatible species with a widespread, but locally patchy distribution.

As a supplement to wild harvest, an American ginseng cultivation industry developed in Wisconsin in the 1900’s

using traditional farming methods. More recently, woods grown techniques have been adopted to produce roots

having an appearance of wild grown plants which command a much higher market price. However, the extent of

these “wild simulated” cultivation practices and their impact on remaining native populations is not well known. In

support of the USFWS and other land management agencies (US Forest Service), scientists at the USGS Leetown

Science Center have been conducting studies to assess genetic diversity, distribution, and population status of

American ginseng using microsatellite marker-based genetic analysis, species distribution modeling, and field

surveys.

In an effort to better understand the distribution, diversity, and abundance of American ginseng, we conducted an

extensive regional survey of suspected wild and known cultivated populations on public and private lands across 13

U.S. states. We developed a set of microsatellite DNA markers for genetic analysis and conducted a variety of

population structure, diversity, and phylogeographic analyses. Our analysis shows that, while relatively diverse,

American ginseng populations are small and heavily structured in natural settings, making them more vulnerable to

extinction. We detected a strong phylogeographic signal in the regional data, but with significant translocation and

admixture of suspected cultivated material, even on public lands. In order to better inform management on four U.S.

National Forests, we recently initiated a more intensive follow-on survey to assess threats to distribution, diversity,

and population viability under current harvest regimes.

American ginseng (Panax quinquefolius L., syn. Panax quinquefolium), a

CITES protected North American native herbaceous species harvested for the

medicinal qualities of the fleshy taproot, primarily for export to Asian markets.

Approximate range of American ginseng (Panax quinquefolius L.) within the

eastern United States of America. American ginseng occurs most readily on

cool, moist hillslopes within closed canopy deciduous forests. Also shown are

public and private protected areas.

Methods (Field Survey):

Our study was designed to contrast American ginseng populations growing on four land ownership types:

public conservation, private conservation, public multiple-use, and private (cultivated lands). We developed

initial species distribution models using known locations, a suite of environmental predictors in GIS, and

logistic regression to determine suitable areas to survey. We initiated field sampling to search for American

ginseng plants, determine population characteristics, and acquire plant material for genetic analysis. Field

sampling was spatially extensive with crews sampling portions of the study area throughout most of the

species’ range (13 U.S. states). At sample sites where American ginseng was found, we counted all plants

according to size class (a rough surrogate for age), and we took genetics samples for 8 plants (on average) per

30 x 30 meter (0.09 ha) plot.

Initial logistic regression-based species distribution model for a

portion of the study area used to help select field sampling sites.

Phab = 1.2931 (intercept) + (slope * 0.0589) – (elevation * 0.0012) +

(% deciduous forest * 0.0181 - (average solar insolation * 0.0129)

Typical sample plot with tapes stretched to form a 30x30m (0.09 ha) survey area.

Leaf tissue samples for a subset of found plants were collected using Whatman FTA®

cards and returned to our laboratory for DNA extraction, PCR, and genotyping

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National Geographic, Esri, DeLorme, NAVTEQ, UNEP-WCMC, USGS, NASA, ESA, METI, NRCAN, GEBCO, NOAA, iPC

00.511.520.25

Miles

Structure Groups

Number of Samples

8

'Appalachian' Type

'Ohio Valley' Type

'Wisconsin/Cultivated' Type

100Km

¹

Program Structure 2.3

(Pritchard et al 2000):

- 914 individuals

- 106 loci

(presence/absence)

- Burn-in 10,000

- 10,000 MCMC reps

- Admixture model

- K=1 to 10, 10 reps each

K = 3 clusters of genetic types

http://link.springer.com/article/10.1007/s12686-012-9653-2

Methods (Genetics):

We developed a suite of 12 microsatellite markers to

characterize and assess genetic diversity within and among

sites (Young et al. 2012). Microsatellites are short, repeated

sequences of non-coding (neutral) DNA, that can

accumulate over time as mutations during DNA replication.

Since these mutations are diagnostic by species (or genus)

but are highly variable, they are excellent markers for

discrimination of populations and individuals. Genotyping

of American ginseng was done using standard PCR

laboratory techniques, an ABI 3130xl Genetic Analyzer,

and allele scoring using ABI’s GeneMapper software. Since

American ginseng is a tetraploid, allele copy frequency

could not be reliably determined, so we scored alleles as

present or absent (0,1) resulting in a 106 character allele

phenotype matrix.

Results:

Overall, we found more plants, and a younger age class

structure on private cultivated lands than on public

conservation, public multiple use, or private conservation

lands. Population sizes and densities were more severely

limited on public multi-use lands where harvest of

American ginseng was allowed.

Among land types, American ginseng populations on public

conservation lands were the most genetically diverse (Ht =

0.158), whereas public multi-use lands were the least (Ht =

0.125). Overall, the partitioning of genetic diversity within

and among populations (Gst = 0.589) is still close to that

expected of natural populations with selfing, gravity

dispersed, and regionally distributed life history

characteristics (Hamrick and Godt 1996).

We surveyed a total of 224 sites across thirteen U.S.

states and we found and sampled American ginseng at

155 (69.2%) of the sites we visited. We analyzed a

variety of genetic diversity, population structuring, and

individual to population relatedness metrics using the

allele phenotype matrix of 914 genetic samples. Allele peak scoring and resulting 106 character phenotype matrix used in analysis.

Mapping predicted genetic structure groups across the species range displays a strong phylogeographic pattern

with one group arrayed north and south along the Appalachian Mountains (“Appalachian type”), a second group

centered in the Tennessee and southern Ohio valleys (“Ohio Valley type”), and a third cluster found in Wisconsin

(“Wisconsin type”), but spread throughout the study area and admixed with the other two types. Known

cultivated plants also group strongly with the Wisconsin type lending support to the hypothesis that these plants

are being widely distributed through commercial availability of Wisconsin seed and root stock, even on public

conservation lands (e.g. National Parks). Furthermore, plants with identical allelic phenotypes were found

between sites within states as well as among states, strongly suggesting human mediated dispersal.

Admixing of these cultivated genotypes with remaining “wild” types has unknown consequences, but has the

potential for deleterious effects such as outbreeding depression. Additionally, the likelihood of so many human

augmented populations has implications for management of American ginseng as a wild species. We are currently

conducting a similarly designed but smaller scale follow-up study including intensive sampling of four U.S.

National Forests with multiple-use mandates and allowed harvest of American ginseng.

American ginseng plants found during field survey arrayed by size class (1

prong = seedling, 2 prong = juvenile, 3 prong = adult, 4 prong = mature

adult), and by land type (PP = Public conservation, PU = Public multi-use,

VP = Private conservation, VU = Private cultivated).

Results from individual-based, genetic population structure analysis showed a distinct phylogeographic pattern and clustering into three groups.

References:

Hamrick, J.L. & Godt, M.J.W. (1996). Effects of life history traits on genetic diversity in plant species. Philosophical Transactions: Biological Sciences, 351 (1345), 1291–1298.Pritchard, J. K., Stephens, M., & Donnelly, P. (2000). Inference of population structure using multilocus genotype data. Genetics, 155, 945–959.Young, J.A. M.S. Eackles, M.J. Springmann, and T.L. King. (2012). Development of tri- and tetra- nucleotide polysomic microsatellite markers for characterization of American

ginseng (Panax quinquefolius L.) genetic diversity and population structuring. Conservation Genetics Resources 4(4): 833-836).

Acknowledgements: We thank Mike Eackles for leadership in laboratory analysis, Marcus Springmann for field sampling and laboratory analysis, and

Chris Walter for GIS support and field sampling. This research was funded by the USGS Science Support Partnership program and by the US Forest

Service. Additional field work was conducted in 2014 by David Siripoonsup, Ian Sabo, Jamie Sparks, and Juliana Hong.