Western Prairie fringed orchid (Platanthera praeclara)

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Western Prairie fringed orchid flower spike
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Western Prairie fringed orchid fact file

Western Prairie fringed orchid description

KingdomPlantae
PhylumTracheophyta
ClassLiliopsida
OrderOrchidales
FamilyOrchidaceae
GenusPlatanthera (1)

A characteristic plant of North American tallgrass prairies, the Western Prairie fringed orchid (Platanthera praeclara) is a beautiful plant with its fate tied to that of its habitat, which has been reduced to less than two percent of its former vast range. Consequently, this elegant wildflower is now classified as Endangered on the IUCN Red List due to the high risk of it becoming extinct (2).

The Western Prairie fringed orchid is best recognised by its showy white flowers, which are borne on a large raceme. Each flower produces a vanilla-like fragrance and has a long nectar spur and a deeply-lobed, deeply-fringed lower petal, or ‘lip’ (3) (4). The raceme sits atop a single, long, smooth stem, which may grow up to 85 centimetres in length (3), but is often as short as 14 centimetres on drought-stressed plants (5). Five to ten leaves branch from the stem (3). The lower leaves, which measure 9 to 15 centimeres in length and 1.5 to 3.5 centimetres in width, are smooth and long, and are larger than the upper leaves (5).

The Western Prairie fringed orchid has thick, fleshy roots with an underground storage organ called the ‘tuberoid’. This swollen part of the roots serves to store energy, so the plant may survive winter and dry periods, as well as to provide nutrients during the growing season (5) (6).

The Western Prairie fringed orchid is often confused with the more common ragged-fringed orchid (Platanthera lacera). However, the ragged-fringed orchid has more elongate petals and narrower, more compact, pale green-white flowers, which are about half the size of those on the Western Prairie fringed orchid (3).

Also known as
Western white-fringed orchid.
Synonyms
Habenaria leucophaea, Platanthera leucophaea.
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Western Prairie fringed orchid biology

The biology of the Western Prairie fringed orchid is both interesting and complex. An herbaceous perennial, it appears above ground from late spring until late summer, when the orchid dies back, the root system surviving underground. Also in late summer, a single bud is produced on a special reproductive stem known as a ‘rhizome’. The bud remains dormant until the following spring, when it develops into the main stem. However, if the bud is damaged or fails to develop, the orchid may fail to grow above ground. The orchid will survive underground and may develop the following year, but if it fails to do so for two consecutive years then the orchid is likely to die. Similarly, if the stem is damaged by fire and there are no dormant buds, the orchid cannot re-grow until the following year (3).

Pollination in the Western Prairie fringed orchid is equally complex. The orchid depends on specific hawk moths to pollinate its flowers. However, the moths are not dependent upon the Western Prairie fringed orchid and can feed upon many different species of plant, meaning rates of successful pollination vary greatly each year. Moreover, the timing of flowering and the length of seed dormancy in the Western Prairie fringed orchid are extremely variable (1)

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Western Prairie fringed orchid range

Historically, the Western Prairie fringed orchid was distributed throughout the western Central Lowlands and the eastern Great Plains of the U.S, where tall grass habitats were found. Presently, it is found in 45 counties in Iowa, Kansas, Missouri, Nebraska, North Dakota, and Minnesota, with the latter three states supporting the majority of the remaining populations (1) (2).

The Western Prairie fringed orchid is also found in Manitoba Province in Canada, where just a single population occupies an area of less than seven square kilometres. Much of this population is found in the Tall Grass Prairie Preserve (1) (4).

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Western Prairie fringed orchid habitat

The Western Prairie fringed orchid occurs almost exclusively in native prairies and sedge meadows, where it prefers higher, drier slopes with moist soil, as well as warm climates. It also prefers to grow in direct sunlight, and rarely flowers in dry areas or in times of drought. The Western Prairie fringed orchid is also found in ditches and alongside roads (1) (3) (7)

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Western Prairie fringed orchid status

The Western Prairie fringed orchid is classified as Endangered (EN) on the IUCN Red List (1).

IUCN Red List species status – Endangered

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Western Prairie fringed orchid threats

Occurring in just two percent of its former range (2), the Western Prairie fringed orchid has declined at an alarming rate, due to a combination of habitat loss and habitat degradation. This species’ native prairie habitat is being increasingly lost to agriculture, as well as to developments for housing and commercial use. The inappropriate management of native prairie can also have devastating effects on the Western Prairie fringed orchid, damaging the plants or altering the ecology of the habitat such that it no longer favours orchids (1) (3). The annual mowing of wild hay presents a further problem to the Western Prairie fringed orchid, as this removes its seed capsules before they are ripe, leading to reproductive failure (1) (3)

Cattle are often allowed to roam free on the Western Prairie fringed orchid’s habitat. The cattle trample and kill many orchids, and, by altering the vegetation of prairies, facilitate the invasion of non-native species. Invasive species, such as the leafy spurge (Euphorbia esula), commonly invade degraded prairie habitat, often out-competing native orchids (1) (3).

An additional threat to the Western Prairie fringed orchid is wildfires. This species is naturally exposed to wildfire at intervals of two to four years, and fire is necessary for the natural regeneration of prairie habitats. However, now that many prairies exists as isolated fragments, natural wildfires may occur less frequently, meaning man-made fires must be used to maintain ecological function. The timing of these fires is absolutely critical, and the misapplication of fire can have a detrimental impact on the growth, reproduction and survival of the Western Prairie fringed orchid. Similarly, extensive periods of drought can also hinder its reproduction, meaning global climate change could have disastrous consequences for this species (1) (3)

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Western Prairie fringed orchid conservation

As with other rare plant species that exist in fragments of the once vast North American prairie ecosystem, the main conservation priority for the Western Prairie fringed orchid is the protection and successful management of its habitat. Several populations of this species are already afforded some protection in reserves, such as in Minnesota, where some 84 percent of orchids are protected, and in North Dakota, where over 90 percent of orchids are found on the Sheyenne National Grassland. However, many populations of the Western Prairie fringed orchid occur on privately owned property, where they are still at risk from habitat conversion and development (1) (3).

The severe decline of the Western Prairie fringed orchid led to it being listed as Endangered in Minnesota in 1984, and later nationally Threatened in 1989, making it illegal to kill or pick this plant in the wild. It was subsequently listed as Endangered under the Species at Risk Act in Canada in 2003, and a Species Action Plan was developed in 1996, detailing the priorities for its conservation (1) (3).

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Find out more

Find out more about the conservation of orchids:

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Authentication

This information is awaiting authentication by a species expert, and will be updated as soon as possible. If you are able to help please contact:
arkive@wildscreen.org.uk

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Glossary

Herb (Herbaceous)
A small, non-woody, seed bearing plant in which all the aerial parts die back at the end of each growing season.
Perennial
A plant that normally lives for more than two seasons. After an initial period, the plant produces flowers once a year.
Pollination
The transfer of pollen grains from the stamen (male part of a flower) to the stigma (female part of a flower) of a flowering plant. This usually leads to fertilisation, the development of seeds and, eventually, a new plant.
Raceme
An inflorescence where the individual flowers all have distinct stalks.
Rhizome
Thickened, branching, creeping storage stem. Although most rhizomes grow laterally just along or slightly below the soil's surface, some grow several inches deep. Roots grow from the underside of the rhizome, and during the growing season new growth sprouts from buds along the top. A familiar rhizome is the ginger used in cooking.
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References

  1. IUCN Red List (April, 2011)
    http://www.iucnredlist.org/
  2. Center for Plant Conservation - Platanthera praeclara (April, 2011)
    http://www.centerforplantconservation.org/collection/cpc_viewprofile.asp?CPCNum=9293
  3. Minnesota Department of Natural Resources - Platanthera praeclara (April, 2011)
    http://www.dnr.state.mn.us/rsg/profile.html?action=elementDetail&selectedElement=PMORC1Y0S0
  4. Ames, D.E. (2005) Orchids of Mannitoba. Native Orchid Conservation Inc, US.
  5. Smith, W.R. (1993) Orchids of Minnesota. University of Minnesota Press, Minneapolis.
  6. Sheviak, C.J. and Bowles, M.L. (2008) Western Prairie Fringed Orchid Platanthera praeclara. Chebucto Community Net. Available at:
    http://www.chebucto.ns.ca/recreation/orchidcongress/Pthra_praeclara.pdf
  7. Coffin, B. and Pfannmuller, L. (1988) Minnesota’s Endangered Flora and Fauna. University of Minnesota Press, Minnesota.
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Image credit

Western Prairie fringed orchid flower spike  
Western Prairie fringed orchid flower spike

© David McAdoo

David McAdoo
ncorchid@yahoo.com
http://www.flickr.com/people/ncorchid/

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