Minnesota Profile: Western Prairie Fringed-Orchid (Platanthera praeclara )

Vital Statistics

This orchid is one of four Minnesota plants listed as federally threatened. It grows in the tallgrass prairies of seven states, but only three have large populations: North Dakota, Manitoba, and northwestern Minnesota, where the former bed of Lake Agassiz in Polk County has plant populations that can number in the thousands. Populations in southeastern and southwestern Minnesota range from a handful to several hundred.

Appearance

A stout, erect, long-lived perennial, it has simple, smooth leaves and a showy spike of up to two dozen white flowers. The lip, or lower petal, of each flower is deeply three-lobed and fringed. Flowers are 1 inch or more in size, with a nectar spur more than 1 inch long. Average height of flowering plants is 18-24 inches.

Identification

In Minnesota this orchid might be confused with the ragged fringed-orchid (P. lacera), characteristic of northern forests. The ragged fringed-orchid's much smaller flowers, more linear fringes, and shorter height distinguish it from the western prairie fringed-orchid.

Habitat

Sites range from small roadside remnants of rich mesic (moist) tallgrass prairie in the southeast, to mesic prairie in the southwest, to wet mesic prairie, aspen parkland, and wet meadows in the northwest.

Life History and Biology

This perennial flowers erratically and the number of plants declines precipitously during extended drought. At dusk the nectar gives off a honeysuckle-like fragrance that attracts pollinators, including specifically adapted nocturnal hawk moths. The pollinator must have a proboscis long enough to reach the nectar at the bottom of the long spur. At the same time, it must bump its forehead against the flower's pollen-bearing body. Seed germination depends on the presence of soil fungi that form a close association with the dust-sized seeds and provide nourishment during an as-yet-unknown number of years before plants appear above ground.

Management

More than 80 percent of Minnesota's western prairie fringed-orchids grow in areas owned by the state or by conservation groups. Most privately owned sites are hayfields. Studies are underway to compare the effectiveness of spring and fall prairie burns, mowing, and hands-off treatments in northwestern Minnesota.

Nancy Sather, DNR Botanist