Plant of the Week
Mountain Lady's Slipper (Cypripedium montanum Douglas ex Lindl.)
By Russell Holmes
Mountain lady’s slipper is in the Orchidaceae (orchid family), one of the largest and most diverse of all plant families. Recent estimates on the number of species in the family have been as high as 35,000 but the actual number of species is uncertain and new species are continually being described. Species are distributed worldwide but most species grow in tropical areas. Economic importance is mostly limited to horticulture but only a relatively few number of species are used in the industry. Orchids produce some of the most magnificent flowers in the plant kingdom and are known for highly specific associations with pollinators. Though mountain lady’s slipper, like most other species in the family, produces beautiful flowers, collection of wild plants is strongly discouraged. Most mountain lady’s slipper populations are very small, can easily be decimated and transplanted wild plants rarely survive. Some states have laws protecting wild orchid populations.
Stems of mountain lady’s slipper arise 2 to 7 dm (8 to 28 inches) from short rhizomes. Leaves are sessile, often sheathing, and generally broadly elliptic in shape, 5 to 15 cm (2 to 6 inches) long and up to 7 cm (2.8 inches) broad. The inflorescence typically includes one to three flowers each subtended by a green leafy bract. The sepals and petals are light to deep brownish-purple. The upper (dorsal) sepal is ovate-lanceolate and 3 to 6 cm (1.2 to 2.4 inches) long. The lower sepal (synsepal) is elliptic to lanceolate, forked (bidentate) at the tip and approximately the same length as the dorsal sepal. Petals are slightly longer than the sepals, 4.5 to 7 cm (1.8 to 2.8 inches) long, narrowly to broadly lanceolate and usually twisted and wavy. The labellum is strongly pouched, 2 to 3 cm (0.8 to 1.2 inch) long, dull white to purple tinged and typically purple veined. There are two fertile stamens on each side of the column that leads to a densely glandular and pubescent ovary.
The range of mountain lady’s slipper extends from southern Alaska through British Columbia and Alberta into the Rocky Mountains of Idaho, Montana and Wyoming. It extends south through the Pacific Northwest states of Washington and Oregon into northern California. Populations east of the Cascade Mountains are much more abundant than those on the Westside. Populations west of the Cascades have decreased since pioneer settlement. Large discontinuities currently exist within the range of the species.
Habitat is extremely variable. Populations most often occur in open mixed conifer or mixed conifer hardwood forests but are also documented in forest openings, shrub thickets and alpine meadows. Moisture regimes vary from dry to moist. Elevation ranges from approximately 500 to 2100 meters (1600 to 6900 feet). Associated tree species include Douglas-fir (Pseudotsuga menziesii), various species of fir (Abies), lodgepole pine (Pinus contorta), Ponderosa pine (Pinus ponderosa), quaking aspen (Populus tremuloides) and oak (Quercus spp.).
Linnaeus was the first to describe the genus Cypripedium. He included all lady slipper orchids in his description which are now divided into four genera. The Lewis and Clark expedition was the first to document mountain lady’s slipper in western North America. They collected a specimen at Weippe Prairie in Clearwater County, Idaho on June 14, 1806. David Douglas collected a specimen from the Blue Mountains of Washington and named it Cypripedium montanum. John Lindley published a scientific description of the Douglas collection in 1840.