Pink Lady Slipper or Moccasin Flower Cypripedium acaule

Introduction

These gorgeous orchids are always a lovely treat when you find them growing in the forest. Fortunately, they are not excessively rare, though they are not all that common either. Cypripedium acaule is part of the Cypripedioideae subfamily in the Orchidaceae family. It goes by two common names the Pink Lady Slipper Orchid or the Moccasin Flower after their slipper or moccasin-shaped flowers that are unique to their genus. Orchids everywhere are declining in population due to habitat loss, climate change, and highly specific pollination with poor overall pollination rates. If you do find these please never pick the beautiful flowers. Instead, leave them there to hopefully be pollinated and produce the next generation. Take out your phone and take pictures of the beautiful flowers instead. You can put them on your computer desktop or print them and frame them for your wall and enjoy them for many years.

Description of Cypripedium acaule

Stem & Leaves

Pink Lady Slippers are erect herbaceous perennials 15 – 60 cm tall with solitary flowers on a leafless peduncle (flower stalk).

Two leaves grow opposite from each other directly from the rhizome. They are ovate or broadly elliptic to oblong in shape and measure 9 – 30 cm long and 2.5 – 15 cm wide. Rarely plants will only have one leaf.

Flowers & Fruits

The showy solitary flowers bloom from April to July. They have tepals (sepals and petals) that are yellowish-brown, reddish-brown, pinkish, or even green. They are deflexed or spreading and may be slightly twisted, and are 1.9 – 5.2 cm long. The lip (labellum) is located below the tepals and is shaped like a large pouch with a slit down the middle, slipper or moccasin-like. It is usually a light pink but occasionally may be magenta and is obovoid in shape, 3 – 6.7 cm long.

Toxicity

The Cypripedium genus all have glandular hairs on the leaves and stems. The compound in the hairs can cause contact dermatitis similar to poison ivy.

Similar Species Frequently Confused With

It is difficult to confuse Cypripedium acaule for most other genera due to the unique moccasin-like lip on the flower. Sometimes people do mistake flowers of other genera, but if you just look for the distinctive labellum or lip that is shaped like a pouch with a slit down the middle, you can tell for certain it is a Cypripedium. So, most misidentifications are with other members of the same genus. Other Cypripedium species can be differentiated as follows:

• Cypripedium reginae Showy Lady Slipper has a more limited range from Saskatchewan east to Newfoundland Island in Canada and the northern US from Minnesota south to Arkansas and east to Maine, but mostly concentrated in the states that border Canada. It is taller, growing to 100 cm, and usually sprouts many stems from the same rhizome. Showy Lady Slipper has more leaves, with 3 – 5 leaves per stem. It also has larger and much more showy white tepals and usually a brighter pink or magenta lip.
• Cypripedium parviflorum Yellow Lady Slipper is another largely eastern North American species that extends to the Canadian Rockies and Arctic in the west and the Rocky Mountains in the US states. Otherwise, it has a very similar eastern range as Cypripedium reginae. It is fairly easy to tell apart, however, since its lip is always yellow.
• Cypripedium candidum Small White Lady Slipper has a limited range and is listed as a Vulnerable species globally. It is rare and endangered in Canada but can be found in the extreme southern parts of eastern Canada from Saskatchewan east to Ontario. In the US, it is also rare and vulnerable and can be found from North Dakota south to Nebraska and east to New York, with some also found from Missouri south to Alabama. It is a much smaller plant, only up to 36 cm tall, and has a smaller lip that is always white.
• Cypripedium montanum Mountain Lady Slipper is another rare vulnerable orchid that is found in the Pacific Northwest from Alaska south to northern California and east to the Alberta Rocky Mountains in Canada and Montana in the US. It is typically found only at high elevations in open forests and subalpine slopes. It grows to 70 cm tall and has 1 – 3 large flowers on top of its stem, and its pouch is always white.

Distribution of Cypripedium acaule

Moccasin Flower is a central and eastern Canadian and eastern USA species. It is not found anywhere else in the world.

In Canada, Cypripedium acaule is found in Alberta, Saskatchewan, Manitoba, Ontario, Quebec, New Brunswick, Nova Scotia, Prince Edward Island, and Newfoundland Island (not Labrador). It may also be present in the Northwest Territories.

In the USA, Pink Lady Slipper is found in Minnesota, Wisconsin, Illinois, Michigan, Indiana, Michigan, Indiana, Ohio, Kentucky, Tennessee, Alabama, Georgia, North & South Carolina, Virginia, West Virginia, Pennsylvania, Delaware, Maryland, Washington DC, New York, New Jersey, Connecticut, Rhode Island, Massachusetts, Vermont, New Hampshire, and Maine.

Habitat & Growing Conditions of Cypripedium acaule

Cypripedium acaule tolerates a wide range of shade and moisture conditions being found in dry to wet forests, shrublands, and slopes, but it prefers partial shade and well-drained slopes. However, it requires highly acidic soils, which is probably why it is often found in pine forests but can be seen in deciduous and mixed woods as well. It is generally found below 1200 m in elevation.

Growing Pink Lady Slipper in Your Garden

Cypripedium acaule is challenging but not impossible to grow yourself if you don’t already have a highly acidic or coniferous forest to plant them in. For a long time, it was believed that it could not be cultivated due to a belief that a fungal association found in the forest was required for germination and growth. However, Pink Lady Slipper is available commercially but is not easy to find as it is more difficult to grow than other species. You will not be able to grow it from seed as special conditions and fungal associations are still required for germination, but once it has true leaves, it can be moved into a garden.

To grow commercially purchased plants of Cypripedium acaule, the only real critical factor is soil pH. It absolutely must be kept below 5.0 to prevent the plants from rotting from the activity of soil microbes that increase above pH 5.0. Anywhere from 4.0 – 4.5 pH is ideal for Pink Lady Slipper. To keep the pH so low, you must grow them in a container so that you can better control the conditions. Use a significant amount of peat moss or pine duff in the soil and use pH-neutral perlite to improve drainage. Tap water should never be used to water them due to the risk of Calcium in the water that would raise the pH. Instead, use rainwater or distilled water mixed with 2 oz of vinegar per gallon.

Other things to consider are where to place the pots. Ideally, morning sun or dappled sunlight under a tree is best. And be sure to sink the pots into the ground in winter or store them in a cold frame.

Wildlife Values of Cypripedium acaule

Native bees routinely visit the flowers.

Status of Cypripedium acaule

Pink Lady Slipper is currently listed as Least Concern on the IUCN Red List. However, as with most woodland plants, the population of mature individuals being found is decreasing.

NatureServe lists Moccasin Flower as Globally Secure, G5.

In Canada, Pink Lady Slipper is considered Locally Secure S5 in Ontario, Quebec, New Brunswick, Nova Scotia, and Prince Edward Island. It is Apparently Secure S4 in Saskatchewan and Newfoundland Island. In Alberta and Manitoba, it is Vulnerable S3.

In the USA, Cypripedium acaule is considered Locally Secure S5 in West Virginia, Virginia, and North Carolina. It is considered Apparently Secure S4 in Kentucky, Tennessee, New York, New Jersey, Delaware, Connecticut, and Georgia. In Alabama, it is considered Vulnerable S3. It is considered Critically Imperiled S1 in Illinois and Indiana. In all other states where it is found, its status is not yet determined.

Traditional or Other Uses of Pink Lady Slipper

Cypripedium acaule Medicinal Uses

Pink Lady Slipper roots were used by the Algonquin for stomachaches, menstrual disorders, kidney and urinary infections, and venereal diseases. Cherokee used the root as an analgesic, anticonvulsive, to treat colds, flu, stomachaches, kidney problems, worms, and ‘female trouble’. Iroquois used them in a decoction as an analgesic and in a poultice for bite wounds. Menominee used it to treat urinary problems and ‘male disorders’. Micmac and Penobscot used the root as a sedative for nervousness. Rappahannock used the dried roots in whiskey as a panacea for general ailments.

Pink Lady Slipper as an Ornamental

Due to the challenges of growing it this plant is only occasionally grown as an ornamental. But for the most serious and dedicated gardeners or orchid lovers, it is a lovely addition to any woodland garden.

Ethical Wildcrafting of Cypripedium acaule

Check the status in your state before harvesting since it is vulnerable in some areas. See the above section on Status. Alternatively, grow it in your garden but do not attempt to harvest wild plants to transplant to your garden as, most likely, you will simply be killing the plant. Instead, buy commercially available plants that have been germinated in an orchid lab.

Generally speaking, I do not recommend wildcrafting this plant in any form. Transplanting has a poor survival rate, and the only other reason for harvesting is the root to be used medicinally. If using this root is part of your traditional heritage, and you want to harvest some, always use the 1 in 20 rule of Ethical Wildcrafting. Harvest the roots of only one in every plant you see in an area where they are locally common.

Wildcrafting and Processing

Use a digging stick to loosen the roots from the soil. Picked roots can be placed in a basket, bowl, or paper bag and brought home for processing. If you are harvesting multiple products on the same day, be sure to label the roots in a paper bag so that you do not confuse different plants.

Roots should be brushed clean of any dirt and then chopped into more manageable pieces before drying. Dried roots are notoriously difficult to cut into smaller pieces once dried.

Once dried, the roots can be stored in a jar for later use. Label your jar with the species name and the date, and I also usually add the location of the harvest for my own reference. Do not grind or crush the leaves or roots until you are ready to use them. This will keep them as fresh as possible to preserve their medicinal properties. When you pre-grind, even if stored in glass jars, this increases the oxidation rate and rapidly degrades the medicinal properties reducing their useful shelf-life.

References and Resources

Canadensys Plant Search https://data.canadensys.net/vascan/search

Dictionary of Botanical Terms – by Lyrae’s Nature Blog https://lyraenatureblog.com/blog/dictionary-of-botanical-terms/

Flora of North America https://eflora.org

iNaturalist Plant Search https://www.inaturalist.org/home

IUCN Red List https://www.iucnredlist.org/

Lady Bird Johnson Wildflower Center https://www.wildflower.org

Native American Ethnobotany http://naeb.brit.org/

NatureServe Explorer https://explorer.natureserve.org/Search

USDA Plants Database https://plants.sc.egov.usda.gov/home

Willis, Lyrae (? Not yet published).  Plant Families of North America. 

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