Photo © Peter Lesica
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Epipactis gigantea Douglas ex Hook.

Giant helleborine

Orchidaceae (Orchid family)

General Description: A leafy, glabrous, perennial herb up to 1.5 m tall, with 1 to several stems from a creeping rhizome. Leaves are numerous, alternate, sessile, and 5-20 cm long. The lower are oval, but the leaves become more lance-shaped further up the stem. Flowers are rather showy and borne singly in a long, narrow, open, mostly one-sided, leafy-bracted inflorescence at the top of the stem. Sepals and upper petals are 1.3-1.7 cm long, greenish-yellow or brownish in color with purple veins. The lip petal is 1.5-2 cm long, greenish with purple veins, and divided into 3 unequal segments. The fruit is an elliptic, drooping capsule 2-2.5 cm long.

Photo © Robert K. Moseley
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Illustration.

Field Identification Tips: A relatively large stature, numerous long clasping leaves, large brownish flowers, and drooping fruits combine to make giant helleborine a distinctive species.

Phenology: Flowers June to August.

Similar Species: Vegetative plants may be confused with some members of the orchid genus Platanthera, or more likely with Maianthemum stellatum, in the lily family, species that can co-occur with giant helleborine. The prominently clasping leaf bases and taller habit of giant helleborine distinguishes it from Maianthemum, and its generally more numerous and larger leaves and taller habit from Platanthera.

Habitat: In general, giant helleborine occurs in moist areas along streambanks, lake margins, seeps and springs. In Idaho it is associated with thermal waters at higher elevations, or cold springs at lower elevations such as along the Snake River.

Global Distribution: From central Mexico northward to Texas and throughout the western United States to southern British Columbia.

Idaho Distribution: Widespread in Idaho: Bonner, Boundary, and Nez Perce counties in northern Idaho; Idaho, Adams, Valley, Boise, Custer, and Lemhi counties in central Idaho; Elmore, Camas, Gooding, Jerome, Twin Falls, and Owyhee counties in southern Idaho; and Clark and Madison counties in the eastern part of the state.

References:

Atwood, D., J. Holland, R. Bolander, B. Franklin, D. House, L. Armstrong, K. Thorne, and L. England. 1991. Utah threatened, endangered, and sensitive plant field guide. U.S. Forest Service, Intermountain Region, Ogden, UT, and other cooperators.

Mancuso, M. 1991. Field investigation of Epipactis gigantea (giant helleborine), a Region 4 sensitive species on the Payette National Forest. Idaho Department of Fish and Game, Conservation Data Center, Boise, ID. 13 pp. plus appendices.

Wyoming Rare Plant Technical Committee. 1994. Wyoming rare plant field guide. USDI Bureau of Land Management; National Park Service; Fish and Wildlife Service; USDA Forest Service, Intermountain Region and Rocky Mountain Region; Wyoming Game and Fish Department; and The Nature Conservancy, Wyoming Natural Diversity Database.