Western Prairie Fringed Orchid

Platanthera praeclara

Description

The western prairie fringed orchid stands as one of the gems of North America's remaining tallgrass prairies. This flowering orchid may grow to 4 ft (120 cm) tall, comparable in height to the surrounding prairie grasses, and may have up to two dozen white to creamy white fringed flowers. It is a perennial which, following winter dormancy, sends up leaves and a flower spike in May. The alternate leaves are lanceolate to linear and are 3.9-7.8 in (10-20 cm) long. The upper leaves are much smaller than the lower. The flowers have extremely long spurs and a deeply fringed three-part lower lip. The flowers become fragrant after sunset and are pollinated by night-flying hawkmoths.

The western prairie fringed orchid forms a species pair with the closely related eastern prairie fringed orchid (Platanthera leucophaea), also listed as a Threatened species. Before P. praeclara was described, the two species were both known as P. leucophaea. They are distinguished by details of flower structure and their pollination mechanics. The western species has larger flowers, and its pollen is deposited on the eyes of a visiting moth; the eastern species places its pollen on the moth's proboscis.

Curiously, the regal appearance of this plant does not attract insects to pollinate the plant during the daylight. Rather, as night descends over the prairie, the orchid's flowers increase its fragrance to attract the roaming moths. Shrouded in this cover of darkness, the long-tongued hawkmoth rises to visit the intoxicating flowers. This moth is unremarkable in appearance and coloration. What's unusual about it is its uniquely evolved tongue for harvesting the orchid's nectar. The orchid's white fringed petals direct approaching moths to the spur and the plentiful supply of nectar it holds. As the moth hovers with its long tongue extended into the spur, two specialized pollen-bearing structures brush pollen onto the eyes of the moth.

The western prairie fringed orchid nectar spur is the longest of any North American orchid. Only those species of hawkmoths with suitable length tongues and properly spaced eyes can act as pollinators.

After attaching to the eyes, the pollen may be deposited upon the next orchid flower the moth visits. This transfer of pollen among orchids results in fertilization and ultimately the production of seeds.

The remarkable relationship between the long-tongued hawkmoth and western prairie fringed orchid has been continuing successfully for centuries until European settlers settled the heartland of North America. They found the tallgrass prairie yielded fertile soils, ideal for raising a variety of crops. Millions of acres of America's prairies were rapidly converted for cropland. Today only about two percent left of the tallgrass prairie remain and less than 40% of the original western prairie fringed orchid populations. Tallgrass prairie has generally been reduced to small islands in a sea of cropland.

The fragmented prairie landscape created by humans poses the greatest obstacle for these insect-oriented orchids. The expanses of cropland act as a barrier for free movement of hawkmoths between different orchid populations, reducing genetic diversity of isolated stands. Pesticide drift from nearby cropland also poses a threat to non-targeted insects such as the hawkmoth. In some areas, hawkmoth numbers are so depleted that only a very small percentage of flowers are pollinated and produce seed.

These remaining tallgrass prairie tracts must also be intensively managed to prevent native trees and shrubs from invading and shading orchids out, or by exotic weeds such as leafy spurge that can displace the orchid and other native prairie vegetation.

Approximately a quarter of known western prairie fringed orchid sites are protected in preserves or other publicly-managed areas. Land managers are concentrating their efforts on meeting the orchid's needs through implementing long-term management plans.

Providing hawkmoth "corridors" of native prairie between orchid populations could offset the immediate threat that faces isolated populations. However, some orchid preserves are isolated tens or even hundreds of miles apart. For these secluded populations, pollinating the plants by hand can buy the orchid some time until their prairie habitats can be rejoined and pollination can be reclaimed by its original masters.

Long-term survival of this tallgrass prairie gem requires not only protecting its habitat but also insuring the survival of the orchid's only means of reproduction, the long-tongued hawkmoth.

Habitat

This orchid grows in tallgrass calcareous silt loam or moist sand prairies; many populations are found in hay meadows. The species requires full sunlight and is vulnerable to natural succession.

Distribution

The western fringed orchid occurred in the plains and grasslands of the central United States, almost exclusively west of the Mississippi River. Its range extended from southern Manitoba (Canada) through North Dakota and Minnesota and south to Oklahoma and Missouri. According to county records, populations have experienced a 60% decline.

Today this orchid is known from about 37 populations in six states: North Dakota, Nebraska, Kansas, Minnesota, Iowa, and Missouri. It also survives in Manitoba, Canada. It is no longer found in South Dakota, and the two populations that were discovered in Oklahoma during the 1970s have not been observed since then.

In North Dakota the western prairie fringed orchid occurs in a single large, scattered population of about 2,000 plants on the Sheyenne National Grassland, in the southeastern counties of Ransom and Richland. This land is administered by the Forest Service and is leased to the Sheyenne Valley Grazing Association for livestock production.

Five populations of the orchid are known to occur in Nebraska. Two small populations (less than 20 plants) are in the western portion of the state: one along a railroad right-of-way and another in the Valentine National Wildlife Refuge in Cherry County. The three other populations are in the eastern part of the state on public land or private land managed for conservation. The largest of these populations contains about 150 plants.

In Kansas, eight populations are known to exist, seven in private hay meadows and one in a University of Kansas research area. Minnesota has six populations in four counties. The largest of these, containing about 500 plants, is protected. In Iowa, there are 13 known populations, containing a total of about 600 plants. Two small populations survive in Missouri.

Threats

The decline of the western prairie fringed orchid was the result of conversion of its prairie habitat to cropland. Although most land conversions have already taken place, this process continues to pose a threat to the species. In the 1970s, the orchid was discovered in four hay meadows in eastern Kansas; they have since been converted to cropland.

Perhaps the greatest continuing threat to this orchid is the intensive mowing of hay meadows. Over 35% of known populations are found on hay meadows. Annual mowing removes the seed capsules before seed can be dispersed, resulting in a gradual decline in the local population. Additional threats to the species are over-grazing by livestock and natural succession.

Conservation and Recovery

In 1996, the Fish and Wildlife Service released a Recovery Plan for the western prairie fringed orchid. The goal of the recovery plan is to increase the amount of critical habitat protected and managed on behalf of the rare orchid. Specific actions include the maintenance of known areas of native prairie in a natural condition, the development of effective management plans for protected sites, additional searches for unknown populations, conducting population monitoring and research, and dissemination of information about the orchid to a wide audience.

The large North Dakota population of the western prairie fringed orchid on the Sheyenne National Grassland is subject to grazing. The orchid occurs on almost half of the leased grazing allotments. While moderate grazing does not appear to have harmed the rare plant as much as conversion of habitat to cropland or hay mowing, management is necessary to prevent overgrazing. The Forest Service is initiating an interim management plan to ensure that livestock grazing on federal land does not adversely effect orchid populations. The recovery plan for the species has recommended federal policies on grazing management. The FWS is also evaluating management policies for the orchid population on the Valentine National Wildlife refuge in western Nebraska to prevent overgrazing or succession from degrading the critical habitat.

Throughout its current range the western fringed orchid receives some degree of protection. Many of the populations, including most of the largest, are on federal or state lands, or private lands that are managed for conservation.

Contact

U.S. Fish and Wildlife Service
Division of Endangered Species
Federal Building
1 Federal Drive
Fort Snelling, Minnesota 55111-4056
Telephone: (612) 713-5360
Fax: (612) 713-5292

References

Bowles, M. L. 1983. "The Tallgrass Prairie OrchidsPlatanthera leucophaea and Cyripedium candidum : Some Aspects of Their Status, Biology, and Ecology, and Implications Toward Management." Natural Areas Journal 3:14-37.

Case, F.W., Jr. 1987. Orchids of the Western Great Lakes Region. Cranbrook Institute of Science, Bloomfield Hills, Michigan.

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

Sheviak, C. J. 1974. "An Introduction to the Ecology of the Illinois Orchidaceae." Illinois State Museum, Scientific Paper 14.

Sheviak, C. J., and M. L. Bowles. 1986. "The Prairie Fringed Orchids." Rhodora 88:267-290.

U.S. Fish and Wildlife Service. 1996. "Platanthera praeclara (Western Prairie Fringed Orchid) Recovery Plan." U.S. Fish and Wildlife Service, Fort Snelling, Minnesota.