Plant of the Week

Map of the United States showing states. States are colored green where pink ladies slipper may be found.
Range map of pink ladies slipper. States are colored green where the species may be found.

pink ladies slipper.
Pink ladies slipper (Cypripedium acaule). Photo courtesy of Susan Trull, U.S. Forest Service.

Pink ladies slipper (Cypripedium acaule Ait.)

By Patricia J. Ruta McGhan

Pink lady's slipper is a large, showy wildflower belonging to the orchid family. It has two opposite basal leaves with conspicuous parallel veins and a large flower at the end of an erect stalk. The flower is magenta to whitish-pink; sometimes the whitish pink flowers will have darker pink venation. Rarely the flower may be all white. This plant grows 6 to 15 inches tall and flowers generally between May and July.

The species name acaule is Latin, meaning, "stem less", referring to the plant’s leafless flowering stem. Another common name for this plant is moccasin flower.

Orchids often have swollen, ball-shaped tubers that were regarded in traditional practices as having medicinal value. The root of lady's slipper was used as a remedy for nervousness, tooth pain, and muscle spasms. In the 1800s and 1900s it, and other orchids, were widely used as a substitute for the European plant valerian for sedative properties.

In order to survive and reproduce, pink lady's slipper interacts with a fungus in the soil from the Rhizoctonia genus. Generally, orchid seeds do not have food supplies inside them like most other kinds of seeds. Pink lady’s slipper seeds require threads of the fungus to break open the seed and attach them to it. The fungus will pass on food and nutrients to the pink lady's slipper seed. When the lady’s slipper plant is older and producing most of its own nutrients, the fungus will extract nutrients from the orchid roots. This mutually beneficial relationship between the orchid and the fungus is known as “symbiosis” and is typical of almost all orchid species.

Pink lady’s slipper takes many years to go from seed to mature plants.  Seed-bearing harvest of wild lady's slipper root is not considered sustainable. Pink lady's slippers can live to be twenty years old or more.

Closeup a pink lady's slipper flower.
Cypripedium acaule. Photo by Thomas G. Barnes, University of Tennessee Herbarium.

Pink lady's slippers also require bees for pollination. Bees are lured into the flower pouch through the front slit, attracted by the flower’s bright color and sweet scent. Once inside, the bees find no reward, and discover that they are trapped, with only one point of escape. Inside the pouch, there are hairs that lead to a pair of exit openings, one beneath each pollen mass. The bee must pass under the stigma, so if it bears any pollen from a visit to another flower, it will be deposited before picking up a fresh load on the way out.

Pink lady’s slipper lives in a variety of habitats, growing in mixed hardwood coniferous forests of pine and hemlock on rocky/mossy slopes, and in semi-open or in deep humus and acidic but well-drained soil under birch and other deciduous trees of eastern United States forests.

For More Information

Plant of the Week

Yellow Marsh Marigold (Caltha palustris).
Yellow Marsh Marigold (Caltha palustris)