|Eastern prairie fringed orchid, prairie fringed orchid, prairie orchis, prairie white-fringed orchid, white-fringed orchid|
|Marlin L. Bowles|
The following Participating Institutions are custodians for this species in the CPC National Collection:
Chicago Botanical Garden
The conservation of Platanthera leucophaea is fully sponsored.
Marlin L. Bowles contributed to this Plant Profile.
P. leucophaea is one of the largest and showiest of the native North American orchids. It is one of at least 200 North American orchid species, and is currently listed as Federally Threatened. This species has declined in the United States by more than 70 percent from original county records. This decline is due mainly to habitat loss for cropland and pasture. The 30 percent of original populations that remain are threatened by non-native species, illegal collection, and continued habitat loss. Most remaining populations are small (fewer than 50 plants), and only about 20 percent of these have adequate protection and management. The species is also found in Canada, but is now known from only 12 populations. (USFWS 1999, Brownell 1984)
Eastern prairie fringed orchid is a perennial orchid, with an upright leafy stem extending up to 40 inches high from an underground tuber. Its leaves sheath the stem, and are 2-8 inches long, elliptical to lance-shaped, and progressively larger toward the stem base. The inflorescence extends above the leaves, with 5-40 creamy white flowers subtended by lance-shaped bracts. The flowers are distinguished by a 3-parted fringed lip 1.5-3 cm long and a nectar spur 1-2 inches long.
This species has a close relative, Platanthera praeclara, which occurs to the west of the Mississippi River. This species is aptly named the Western prairie fringed orchid, and each have somewhat different flower morphologies, likely because they evolved in the presence of different pollinator species. (Sheviak and Bowles 1986)
Distribution & Occurrence
The eastern prairie fringed orchid requires full sun for optimum growth and reproduction. It occupies tallgrass silt-loam or sand prairies, sedge meadows, fens, lakeshore grasslands, and occasionally sphagnum bogs in the eastern part of its range. (USFWS 1999)
These habitats occur across six physiographic regions. The unglaciated Ozark region supports sedge meadow habitat, from which Platanthera leucophaea is apparently extirpated. Kansan glacial soils support prairie habitat, primarily west of the Mississippi River. East of the Mississippi River, Wisconsinan glacial soils support prairie, sedge meadow, and peatland habitat. The lake plains of the Lake Michigan, Lake Huron, and Lake Erie basins support prairie habitat. Disjunct eastern populations also occur in unglaciated sedge meadow, and formerly occurred in unglaciated prairie in Oklahoma.
|As stated in the U.S. Fish and Wildlife Service's Recovery Plan:
The eastern prairie fringed orchid has declined more than 70% from original county records in the United States.
Most remaining habitats are small, with fewer than 50 plants, and are not representative of the once vast prairie populations of this orchid.
A few populations, primarily in successional vegetation, number in the hundreds or thousands.
About 60 populations are extant in Iowa, Wisconsin, Illinois, Michigan, Ohio, Indiana, and Maine.
Plants have not been relocated in New York, Pennsylvania, New Jersey, or Oklahoma.
Conservation, Ecology & Research
Both high precipitation levels and fire have been suggested to promote flowering of Platanthera leucophaea in tallgrass prairie habitat, but moisture levels appear to be an overriding factor. Over a twelve-year period in Illinois, percent flowering in P. leucophaea populations was higher in wetland habitat and was positively correlated with growing season rainfall. Over time, flowering plants also appeared more quickly in wetland habitat after a severe 1988 drought. Thus, burning would most likely promote flowering in tallgrass prairie wetlands or during years of high growing season rainfall.
White fringed orchids require hawkmoth (SPHINGIDAE) pollination for sexual reproduction. The flowers are nocturnally fragrant and place pollinia on the proboscises of hawkmoths as they ingest a high-volume nectar resource from long nectar spurs. As in most orchids, the flowers are morphologically adapted to outcrossing, but plants appear to be self-compatible and probably receive high levels of self-pollination in small populations when pollinators revisit inflorescences. (Bowles 1983, 1985)
Specific requirements for Platanthera leucophaea seedling establishment are not well known. Seed germination may be light-inhibited, with dormancy broken by darkness and moist stratification; but successful seedling establishment requires mycorrhizal development with a favorable soil-inhabiting fungus. Seedlings may persist for several years as subterranean protocormbs, receiving nutrients from the fungus. This relationship becomes symbiotic once the plants can produce leaves, and it is likely not species-specific for orchids or fungi.
Disturbance may be important in Platanthera leucophaea seedling establishment. Patch disturbance regimes or early-successional vegetation stages are critical for seedling establishment of disturbance-adapted plants, and terrestrial orchids are well known for colonization following disturbance. Platanthera leucophaea populations reach highest densities in disturbed habitats or early- to mid-successional plant communities. Soil fungi responsible for orchid seedling establishment might also respond to similar disturbance or successional patterns. Under apparently favorable conditions or in successional habitats, flowering P. leucophaea have appeared as soon as 5 years after seed dispersal.
The root systems of terrestrial orchids are reduced, and evidently require mycorrhizae for proper water uptake and nutrition especially under stress. (Annual tuber regeneration in orchids may also require reinfection by mycorrhizae. Thus the stability of orchid populations is closely related to the ecological conditions of their mycorrhizae, which may be in part regulated by the increased mycorrhizal productivity that occurs after spring burning of prairie. This relationship is dynamic; orchids occasionally enter dormancy (possibly with mycorrhizal nutrition), or decline as mycorrhizae become reduced. Although Platanthera leucophaea is pre-adapted to dormant season disturbances such as prairie fires, growing season damage to vegetative material may weaken plants by limiting food storage.
Most Platanthera leucophaea populations have been lost through destruction and modification of habitat - primarily conversion of habitat to cropland and pasture.
Alteration of hydrology, fire protection, and development
Genetic surveys using allozyme and RAPDs techniques have found that populations may have relatively high levels of genetic diversity, and that genetic differentiation may occur among populations.
Demographic monitoring has shown that most plants have a short life-span, often flowering only once. As a result, seed production appears to be an important life history stage and demographic process in population maintenance.
Research on reproductive biology is examining how different levels of outcrossing affect seed production and seed viability, and how seed production (when enhanced by hand pollination) may affect the longevity of individual plants. (Vitt 2000)
Reintroduction using dispersal of seeds from hand pollinated plants has shown that flowering plants may appear in as few as three years. (Packard 1991; Keibler 1994, 1995, 1998, 2000)
Laboratory work has identified mycorrhizal fungi species associated with plants, and has developed techniques for propagating seedlings in association with these soil fungi. (Zettler et a. 2001)
Management to reduce invasion by alien species, primarily smooth buckthorn, has used cutting and application of herbicides.
Some hydrology management has focused on removal of drain tiles to restore original drainage.
More research is needed to understand the relationship between mycorrhizal fungi and the longevity of orchids.
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Correll, D.S. 1950. Native orchids of North America north of Mexico. Waltham, MA: Chronica Botanica Co.
Homoya, M.A. 1991. Orchids of Indiana. Indianapolis, Indiana: Indiana Academy of Science.
Luer, C.A. 1975. The native orchids of the United States and Canada excluding Florida. New York: The New York Botanical Garden. 361p.
Zanoni, T.A.; Gentry, J.L., Jr.; Tyrl, R.J.; Risser, P.G. 1979. Endangered and threatened plants of Oklahoma. Norman: University of Oklahoma and Oklahoma State University. 64p.