CPC National Collection Plant Profile

Isotria medeoloides


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CPC National Collection Plant Profile

Isotria medeoloides

Common Names: 
Small Whorled Pogonia, Lesser Five Leaves, Little Five Leaves
FrederickTraugott Pursh, C. S. Rafinesque-Schmaltz
Growth Habit: 
CPC Number: 


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Isotria medeoloidesenlarge
Image Owner: New England Wildflower Society

Isotria medeoloidesenlarge
Image Owner: New England Wildflower Society

Isotria medeoloides is Fully Sponsored
Primary custodian for this plant in the CPC National Collection of Endangered Plants is: 

Isotria medeoloides

Isotria medeoloides is a small, perennial orchid of deciduous forests with a grayish-green, smooth stem up to 30 cm tall that bears at its summit a whorl of 5-6 light-green, elliptical, pointed leaves and 1-2 yellow-green flowers. This distinctive leaf whorl gives the plant its name; only one other co-occurring orchid, its close relative Isotria verticillata, looks similar but has a purplish stem and the stem (peduncle) bearing the ovary is longer than the ovary. The species name, "medeoloides," refers to the resemblance between seedlings of the orchid and the Indian cucumber, Medeola virginiana. However, the lily Medeola has very different flowers and a solid, slender stem, in contrast to I. medeoloides which has a stout, hollow stem.

Often cited as "the rarest orchid east of the Mississippi," this orchid is critically imperiled in 14 (78%) of the 18 states and provinces in which it still occurs; it is thought to be historical or extirpated in 5 states. Nowhere is it considered secure or common. The primary threat to its existence is destruction of its woodland habitat for development or forestry. The majority of its populations typically number fewer than 25 plants, and are thus vulnerable to local extinction. New searches for the plant have turned up new locations in the past decade, however, and ongoing management experiments are revealing much about its biology and the best methods for its conservation.

Distribution & Occurrence

State Range
District of Columbia
New Hampshire
New Jersey
New York
North Carolina
Rhode Island
South Carolina
West Virginia
State Range of  Isotria medeoloides
  Isotria medeoloides inhabits semi-open, mesic forests of eastern North America. Mehrhoff (1988) describes these as mixed deciduous forests in second- or third-growth successional stages. Soils in sites with the orchid are highly acidic, and many are fragipans on shallow-to-bedrock (or shallow-to-clay) slopes of 8-22% where lateral water drainage from upslope sources occurs (NatureServe 2001), particularly in the northeastern part of its range. There, associated species include ferns, club mosses, low-lying evergreen forbs such as partridgeberry (Mitchella repens), a shrub layer of witch hazel (Hamamelis virginiana), and frequently a canopy of paper birch (Betula papyrifera) (NatureServe 2001). Several other orchid species can co-occur with I. medeoloides. Occasionally, the orchid can be found in more calcium-rich sites, including limestone areas in New York, Missouri, and Ontario, where a more species-rich assemblage of herbaceous plants are associated with the orchid. In Georgia, the species is described from partially shaded gaps in mixed hardwood-conifer forests with an open understory and sparse herbaceous layer. Chestnut oak (Quercus prinus), tuliptree (Liriodendron tulipifera), and white or Virginia pine (Pinus strobus or P. virginiana) predominate in the canopy, with blueberry species, New York fern (Thelypteris novaboracensis), and the look-alike Medeola virginiana on the forest floor (Patrick et al. 1995). Some sites have historically supported agriculture, and forest stands overlying Isotria medeoloides vary from 30 to over 75 years in age (von Oettingen 1992). The orchid is frequently found where leaf litter and decaying wood abound. Braided channels of vernal streams are promising places to search (Van Alstine et al. 1996).

Recently, specific habitat models for the plant have been constructed using geographic information systems that combine features such as elevation, soil type, forest composition, and light availability, helping to better predict where the orchid might occur. Such a model by Casabona and Giles (2001) correctly predicted the majority of known locations for the orchid in Prince William Forest Park, Virginia. Sperduto and Congalton (1996) and the U. S. Fish and Wildlife Service (2001) have also refined the habitat "search image" for I. medeoloides, contributing to more precisely targeted searches. For example, nine new populations of I. medeoloides found in Maine and New Hampshire using Sperduto and Congalton's model.

Evidence from field studies suggests that Isotria medeoloides responds favorably to increased light levels and that reproduction may be suppressed by a closing canopy (Mehrhoff 1980, 1988, Brackley 1991). Management to thin the canopy over subpopulations of the orchid in New Hampshire has stimulated flowering, reduced the proportion of plants entering dormancy, and has fostered a higher density of stems (New England Wild Flower Society 1998, Brumback 2003).

  Isotria medeoloides is found along the Appalachian belt from Ontario through New England, south to Tennessee, Georgia, and South Carolina, and west to Michigan (NatureServe 2003). The three primary population centers are uplands eastern New England, the Blue Ridge Mountains, and the coastal plain/piedmont provinces of Virginia (Harvill 1977, von Oettingen 1992).

Number Left
  Approximately 104 populations known (NatureServe 2001), centered on the eastern seaboard with outlying populations in Ontario and Michigan. While no estimates are available on the total number of plants in North America, based on average population size, it is likely to total under 5,000 plants.


Global Rank:  
Guide to Global Ranks
Federal Status:  
Guide to Federal Status
Recovery Plan:  

State/Area Protection
  State/Area Rank Status Date  
  Connecticut S1 E  
  Delaware S1.1  
  District of Columbia SX  
  Georgia S2  
  Illinois S1  
  Maine S2 E  
  Maryland SH  
  Massachusetts S1 E  
  Michigan S1  
  Missouri SH  
  New Hampshire S2 E  
  New Jersey S1  
  New York SH  
  North Carolina S1  
  Ohio S1  
  Ontario S1  
  Pennsylvania S1  
  Rhode Island S1 E  
  South Carolina S1  
  Tennessee S1  
  Vermont SH E  
  Virginia S2  
  West Virginia S1  

Conservation, Ecology & Research

Ecological Relationships
  Isotria medeoloides plants may live for several years, remaining dormant for several years at a time (Mehrhoff 1989, Vitt 1991). Plants that remain dormant more than three years have a small probability of re-emerging (Vitt 1991). With few specialized structures or scents to attract insect pollinators, plants appear to be primarily self-pollinating (Mehrhoff 1983). Seed production is characterized as low to moderate, with 9,600 seeds produced by one plant (Mehrhoff 1983), but reproduction is generally efficient due to the orchid's capacity for self-fertilization (Vitt and Campbell 1997). Although multiple stems can arise from a single rootstock, Isotria medeoloides does not reproduce vegetatively (Mehrhoff 1983). Taller plants with a larger whorl diameter tend to flower more frequently than smaller plants (Mehrhoff 1989), and may emerge somewhat earlier in the year (Brumback and Fyler 1988). Plants emerge in May at the northern edge of the orchid's range, and in April farther south. Flowers can be maintained from several days to two weeks (Homoya 1977, Mehrhoff 1983). The fruit capsule matures in the fall. Dust-like orchid seeds often disperse by wind from the parent plant, but precise dispersal mechanisms are undescribed for this species.

  Conversion of woodland habitat for housing, industrial, or highway development (von Oettingen 1992) is identified as the primary factor in loss of populations
Overcollection for horticultural or research purposes has been cited as a secondary threat (von Oettingen 1992)
Trampling by recreational use of sites (von Oettingen 1992)
Herbivory by deer (Ware 1991), slugs (Brumback and Fyler 1988), or insects (Ware 1989)
Clear-cutting that fragments habitat (Brackley 1991). Many areas identified as potential habitat in one New Hampshire survey had already been logged.
Canopy closure that substantially reduces light availability, or conversely, canopy opening that stimulates growth of an understory layer that can outcompete the orchid is identified as a potential threat (Brackley 1991, Brumback 2003).

Current Research Summary
  The New England Wild Flower Society (Framingham, Massachusetts) has monitored the responses of Isotria medeoloides to experimental canopy thinning at one New Hampshire site since 1997. Likewise, plants have been followed at the site since the early 1980's (Brumback and Fyler 1988, Brumback 2003).
Dr. Donna Ware, Professor of Biology at the College of William and Mary (Williamsburg, Virginia) has been conducting long-term studies of the orchid (contact dmware@wm.edu).
Dr. Lawrence Zettler (Department of Biology, Illinois College, 1101 West College Avenue, Jacksonville, Illinois 62650, USA), a research associate at the Marie Selby Botanical Gardens in Florida, is studying mycorrhizal interactions in Isotria medeoloides.
Dr. Pati Vitt (Chicago Botanic Garden, pvitt@chicagobotanic.org) conducted part of her graduate research on the demography of Isotria medeoloides.

Current Management Summary
  The New England Wild Flower Society, in cooperation with the U. S. Fish and Wildlife Service, is conducting experimental canopy thinning and long-term population monitoring at a site in East Alton, New Hampshire, with considerable success (see above).
The U. S. Marine Corps hosts one of North America's largest populations of Isotria medeoloides on their Quantico Base in Virginia. They plan military exercises and timbering operations in collaboration with the U. S. Fish and Wildlife Service so as not to threaten the population, and Base Natural Resource specialists monitor the plants annually (U. S. Marine Corps 2001).

Research Management Needs
  Identify mycorrhizal associates and their impacts on seed germination, seedling establishment, habitat needs, and viability of populations
Understand patterns of dormancy, specifically environmental factors causing plants to enter and recover from dormancy and means to predict which stems will enter dormancy
Study seedbanking and seed viability in the field
Determine patterns of genetic relatedness among colonies, populations, and the primary population centers and outlier sites for the orchid across its range
Develop consistent methods for monitoring populations quantitatively across the species' range
From existing long-term demographic data and new studies of marked plants, develop a population viability analysis and predict minimum viable population size for the orchid so that protection strategies can target the most vital and healthy populations
Conduct systematic surveys for the orchid using refined habitat models
Determine the impacts of herbivores on plant survivorship and reproduction
Characterize collateral impacts of research visits on plant vigor and reproduction
Implement habitat management such as moderate canopy thinning where succession appears to be inhibiting plant growth and reproduction.

Ex Situ Needs
  Develop techniques for propagation of Isotria medeoloides, both to reduce collecting pressures on existing wild populations and to provide stock for population augmentation if needed (note: one transplantation effort to date has been largely unsuccessful [Brumback and Fyler 1996]).


Books (Single Authors)

Correll, D.S. 1950 (revised1978). Native Orchids of North America North of Mexico. Stanford, California: Stanford University Press. 400p.

Luer, C.A. 1975. The Native Orchids of the United States and Canada Excluding Florida. Bronx, New York: New York Botanical Garden. 361p.

Books (Sections)

Ware, D.M.E. 1991. Small whorled pogonia. In: K. Terwilliger (Coordinator), editor. Virginia's Endangered Species. Nongame and Endangered Species Program, Virginia Department of Game and Inland Fisheries. The McDonald and Woodward Publishing Company. Blacksburg, Virginia. p 95-97.

Books (Edited Volumes)

1922 A discussion of Pogonia and its allies in the northeast United States with references to extra-limital genera and species. Orchidaceae. 3-38p.

Brumback, W. E. and C. W. Fyler. 1996 Small whorled pogonia (Isotria medeoloides) transplant project. D. A. Falk, C. I. Millar, and M. Olwell (Editors), Restoring Diversity: Strategies for Reintroduction of Endangered Plants. Washington, D. C: Island Press. 445-451p.

Electronic Sources

Casabona, G.; Giles, R.H. Jr. (2001). A Computer Map of Potential Sites for the Small Whorled Pogonia (Isotria medeoloides) in Prince William Forest Park (A National Park). Virginia Polytechnic Institute and State University Blacksburg, Virginia. http://fwie.fw.vt.edu/rhgiles/richholewild/Isotria.htm. Accessed: 2003.

COSEWIC. Profile on Canadian Species At Risk for Isotria medeoloides. http://www.speciesatrisk.gc.ca/search/speciesDetails_e.cfm?SpeciesID=194.

Massachusetts Natural Heritage and Endangered Species Program. (1993). Small whorled pogonia (Isotria medeoloides (Pursh) Raf.). Massachusetts Endangered Plants Fact Sheet. Division of Fisheries and Wildlife. http://www.state.ma.us/dfwele/dfw/nhesp/nhfacts/Isomed.pdf.

NatureServe. (2008). NatureServe Explorer: An online encyclopedia of life [web application]. [Internet].Version 7.0. NatureServe, Arlington, Virginia. http://www.natureserve.org/explorer. Accessed: (June 17, 2008).

New England Wild Flower Society. (1998). Research report. http://www.newfs.org/researchreport.htm. Accessed: 2003.

Patrick, T.S.; Allison, J.R.; Krakow, G.A. (1995). Protected plants of Georgia, an information manual on plants designated by the State of Georgia as Endangered, Threatened, Rare or Unusual. Georgia Department of Natural Resources, Wildlife Resources Division, Georgia Natural Heritage Program. http://georgiawildlife.dnr.state.ga.us/assets/documents/isotme.pdf. Accessed: 2003.

U. S. Fish and Wildlife Service. (2001). Small whorled pogonia habitat model. http://r5gomp.fws.gov/gom/habitatstudy/metadata/small_whorled_pogonia_model.htm. Accessed: 2003.

U. S. Marine Corps. (2001). Small whorled, big mission. Poster in the series, "Marines: We're saving a few good species.". http://endangered.fws.gov/photos/posters/Pogonia.pdf. Accessed: 2003.

United States Fish and Wildlife Service. (2001). Species profile for Isotria medeoloides. Includes links to all relevant documents regarding listing and de-listing of the species. http://endangered.fws.gov/i/q/saq1q.html.

United States Fish and Wildlife Service. (2001). Species profile for Isotria medeoloides. Includes links to all relevant documents regarding listing and de-listing of the species. https://ecos.fws.gov/species_profile/SpeciesProfile?&spcode=Q1XL.

USDA, NRCS Plants National Database. Search on Isotria medeoloides for excellent information on the biology and distribution of this species. Excellent photographs of the plant are available at this site. http://plants.usda.gov/plants.

von Oettingen, S.L. (1992). Small whorled pogonia (Isotria medeoloides) recovery plan, first revision. U.S. Fish and Wildlife Service. Technical/Agency Draft. Newton Corner, MA. 68p. http://ecos.fws.gov/docs/recovery_plans/1992/921113b.pdf. Accessed: 2003.

Journal Articles

Brackley, F.E. 1985. The orchids of New Hampshire. Rhodora. 87: 1-117.

Brumback, W.E.; Fyler, C.W. 1988. Monitoring of Isotria medeoloides in New Hampshire. Wild Flower Notes. 3: 32-40.

Case, F.W. Jr.; Schwab, W. 1971. Isotria medeoloides, the smaller whorled pogonia, in Michigan. Michigan Botanist. 10: 39-43.

Harvill, A.M. Jr. 1977. Isotria medeoloides on the Piedmont of Virginia. Rhodora. 71: 303-304.

Keeman, P.E. 1988. Progress report on Isotria medeoloides. American Orchid Society Bulletin. 57: 624-626.

Mehroff, L.A. 1983. Pollination in the genus Isotria. American Journal of Botany. 70: 1444-1453.

Mehroff, L.A. 1988. Reproductive vigor and environmental factors in populations of an endangered North American orchid, Isotria medeoloides (Pursh) Rafinesque. Biological Conservation. 47: 281-296.

Mehroff, L.A. 1989. The dynamics of declining populations of an endangered orchid, Isotria medeoloides. Ecological Publications of Ecological Society of America. 70: 783-786.

Sperduto, M.B.; Congalton, R.G. 1996. Predicting rare orchid (small whorled pogonia) habitat using GIS. Photogrammetric. Engineering and Remote Sensing. 62: 1269-1279.

Stuckey, I. 1967. Environmental factors and the growth of native orchids. American Journal of Botany. 54: 232-241.

U. S. Fish and Wildlife Service. 1994. Final rule to reclassify the plant Isotria medeoloides (small whorled pogonia) from endangered to threatened. Federal Register. 59, 193: 50852-50857.

Van Alstine, N.E.; Moorhead, W.H. III; Belden, A. Jr.; Rawinski, T.J.; Ludwig, J.C. 1996. Recently discovered populations of small whorled pogonia (Isotria medeoloides) in Virginia. Banisteria. 7: 3-7.

Vitt, P.; Campbell, C.S. 1997. Reproductive biology of Isotria medeoloides (Orchidaceae). Rhodora. 99: 56-63.


Brackley, F.E. 1991. 1991 census of Isotria medeoloides for the State of New Hampshire. Unpublished report to the New Hampshire Natural Heritage Inventory, Concord, New Hampshire. Concord, New Hampshire: New Hampshire Natural Heritage Inventory. p.32.

Brownwell, V.R. 1981. A status report on the small whorled pogonia (Isotria medeoloides) (Pursh) Raf.). Toronto, Ontario, Canada: Ontario Ministry of Natural Resources. p.38.

Brownwell, V.R.; White, D.J. 1998. Updated COSEWIC Status Report on the Small whorled pogonia, Isotria medeoloides. Toronto, Ontario, Canada: Committee on the Status of Endangered Wildlife in Canada, Ontario Ministry of Natural Resources. p.13.

Brumback, W.E. 2003. Monitoring and habitat management actions for Isotria medeoloides (small whorled pogonia) at E. Alton, New Hampshire during 2002. Unpublished report. Framingham, Massachusetts: New England Wild Flower Society.

Ware, D.M.E. 1989. The population ecology of Isotria medeoloides in Virginia with comparisons with I. verticillata, 1988 season. Unpublished report. Richmond, Virginia: Virginia Department of Agriculture, Bureau of Plant Protection and Pesticide Regulation. p.34. SWP-DW-2.


Homoya, M. A. 1977. The Distribution and Ecology of the Genus Isotria in Illinois. [M. Sc. Thesis]: Southern Illinois University. Carbondale, Illinois. 104p.

Mehrhoff, L. A. 1980. The Reproductive Biology of the Genus Isotria (Orchidaceae) and the Ecology of Isotria medeoloides. [M. A. Thesis]: University of North Carolina. Chapel Hill, North Carolina. 65p.

Sperduto, M. B. 1993. Use of a GIS to Predict Potential Habitat for Isotria medeoloides (Pursh) Raf. in New Hampshire and Maine. [M. Sc. Thesis]: University of New Hampshire. Durham, New Hampshire. 106p.

Vitt, P. 1991. Conservation of Isotria medeoloides: a Federally Endangered Terrestrial Orchid. [M. Sc. Thesis]: University of Maine. Orono, Maine. 40p.

  This profile was updated on 3/4/2010
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