Cypripedium acaule is widespread in eastern North America and is abundant and common in the eastern and northeastern parts of its range.
Cypripedium acaule can be found from Alberta, Saskatchewan, and Manitoba across southern Ontario and Quebec, the Great Lakes region and from Newfoundland down the east coast of the United States to the central Georgia Piedmont and west to Alabama and Tennessee.
The species occurs in USA [Alabama (S3), Connecticut (SNR), Delaware (S4), District of Columbia (SNR), Georgia (S4), Illinois (S1), Indiana (S3), Kentucky (S4), Maine (SNR), Maryland (SNR), Massachusetts (SNR), Michigan (SNR), Minnesota (SNR), New Hampshire (SNR), New Jersey (S4), New York (S4), North Carolina (S5), Ohio (SNR), Pennsylvania (SNR), Rhode Island (S4), South Carolina (SNR), Tennessee (S4), Vermont (SNR), Virginia (S5), West Virginia (S5), Wisconsin (SNR)) and Canada [Alberta (S3), Manitoba (S4), New Brunswick (S5), Newfoundland Island (S4), Northwest Territories (SNR), Nova Scotia (S5), Ontario (S5), Prince Edward Island (S5), Quebec (S5), Saskatchewan (S4?)].
The extent of occurrence (EOO) is estimated at 2,789,117 km ² and the area of occupancy (AOO) is estimated at 2,848 km ².
The species can be found from sea level up to 1,200 m altitude.
Sources for distribution information: Cribb 1997, Frosch and Cribb 2012, Gupton et al. 1986, Homoya 1993, Kartesz 1994, Luer 1995, Meades et al. 2000, Patrick et al. 1995, Pepoon 1927 and Sheviak 1974.
Regularity: Regularly occurring
Regularity: Regularly occurring
Global Range: Wide range: from Alberta, Saskatchewan, and Manitoba across southern Ontario and Quebec, surrounding the Great Lakes region and from Newfoundland down the east coast of the United States to the central Georgia Piedmont.
Habitat and Ecology
Cypripedium acaule occurs in a variety of habitats from dry forests, especially pine woods, often in humus mats covering rock outcrops, to moist woods, bogs, swamps, brushy barrens, heath, and roadsides. The species also grows in deciduous woods and mesic white pinewoods.
Cypripedium acaule prefers sandy soil, rich in humus, strongly acidic and aerated. The species grows in moderate shade and well-drained slopes. It flowers from April to June.
Sources: Cribb 1997, Frosch and Cribb 2012, Gupton et al. 1986, Homoya 1993, Kartesz 1994, Luer 1995, Meades et al. 2000, Patrick et al. 1995, Pepoon 1927, and Sheviak 1974.
Flower-Visiting Insects of Pink Lady's Slipper in Illinois
(bees and other insects are lured to the showy and fragrant flower of this orchid by deception, as it provides neither nectar nor accessible pollen; the moth was resting on the lip of the flower; observations are from Plowright et al., Davis, Stoutamire, and Barrett & Helenurm; according to Davis, pollinators are primarily queen bumblebees)
Apidae (Bombini): Bombus spp. exp (Dv), Bombus borealis exp (Stm), Bombus vagans exp (Plw, Stm, BH), Psithyrus ashtoni exp (Dv); Anthophoridae (Anthophorinae): Anthophora terminalis exp np (Stm)
Halictidae (Halictinae): Augochlorella striata exp np (Stm)
Syrphidae: Rhingia nasica exp fq np (Stm)
Geometridae: Tetracis cachexiata rst np (Stm)
Staphylinidae: Eusphalerum spp. fq exp np (BH)
Life History and Behavior
Molecular Biology and Genetics
Barcode data: Cypripedium acaule
Statistics of barcoding coverage: Cypripedium acaule
Public Records: 1
Specimens with Barcodes: 1
Species With Barcodes: 1
IUCN Red List Assessment
Red List Category
Red List Criteria
Cypripedium acaule is widespread with a large distribution area and abundant populations. The extent of occurrence and area of occupancy of the species are greater than 20,000 km2 and 2,000 km2 respectively. The existing threats to the species and its habitats are unlikely to cause populations to decline quickly in the near future and the future of the species would be secured if the conservation measures suggested are applied and public awareness is raised. The species is still so common that only a high level of collecting would impact populations beyond a very local scale. Therefore, Cypripedium acaule is assessed as Least Concern.
National NatureServe Conservation Status
Rounded National Status Rank: N5 - Secure
Rounded National Status Rank: N5 - Secure
NatureServe Conservation Status
Rounded Global Status Rank: G5 - Secure
Reasons: Cypripedium acaule has a wide range in eastern Canada and the United States, and is common in parts of this range. It is found in bogs and swamps, and also in drier oak or coniferous woodlands in acidic soil (Homoya 1993). Threats include exploitation for horticultural or medicinal purposes and habitat loss in parts of its range (Homoya 1993; Deborah White, pers. comm. 2002).
Cypripedium acaule is very common in the acidic soil regions of New Brunswick, Nova Scotia, Prince Edward Island central Ontario and many sites on the Cumberland Plateau.As far as population size is concerned; Illinois - very small and continuing downward. There is only one small subpopulation - maybe half a dozen plants in all - remaining in Illinois, and that subpopulation is currently threatened by invasion of Rosa multiflora and Rhamnus cathartica. The species was only recorded from four counties in Illinois: Polk, Cook, Lake and McHenry. As late as the 1940s, they were not uncommon in the Chicago region (Laura Rericha, Cook County Forest Preserve ecologist, personal communication) until the expansion of urban areas. There was one small wetland subpopulation in suburban Glen Ellen, Illinois until it was destroyed when a park was built on its location. Virginia - Rockingham County, Virginia. A 37 year project began in 1977, annual censuses, landscape-scale and pollination experiments continue (Gill 1989, 1996). Data are being compiled and computerized. Initially 5,453 genets, 6,120 ramets, sharply declining since 1999.
Cypripedium acaule is under numerous anthropogenic threats including exploitation for horticultural or medicinal purposes, habitat loss and disturbance in parts of its range due to urbanization and continued real estate development (Pepoon 1927), competition from exotics such as Japanese Honeysuckle, uncontrolled incursion of native and non-native brushy species into the habitat, climate change and alteration of forest habitat through fire suppression
Cypripedium acaule is a popular subject for collection for sale for uses both horticultural and medicinal. The roots of C. acaule have been used as a sedative, and it is reportedly being sold by "a few companies" despite the 1988 request by the American Herbal Products Association that its members cease using wild-harvested Cypripedium (Medicinal Plant Working Group 2002).
Comments: Threats include habitat destruction (especially new construction) and disturbance, such as competition from exotics such as japanese honeysuckle or alteration of forest habitat through fire suppression (Patrick et al. 1995). Though Cypripedium acaule is advertised by several distributors as available laboratory-propagated, exploitation of wild populations has occurred in the past (Patrick, et al. 1995) and the plants continue to be actively collected for sale (Deborah White, pers. comm. 2002, Al Schotz, pers. comm., 2002). Uses are apparently both horticultural and medicinal. The roots of C. acaule have been used as a sedative, and it is reportedly being sold by "a few companies" despite the 1988 request by the American Herbal Products Association that its members cease using wild-harvested Cypripedium (Medicinal Plant Working Group 2002). In addition, the species is showy and a popular subject for sale in large commercial growers' outlets (often the roots and rhizomes of these plants are sold in such poor condition and the plants will not survive). In some areas, natural populations may be devastated by these unethical practices (Tom Patrick, pers. comm., 2002). At least in eastern Canada, however, the plant remains so common that only a "massive" amount of collecting would impact populations beyond a very local scale (Sean Blaney, pers. comm. 2002).
All orchid species are included under Appendix II of the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES).
Cypripedium acaule is listed by the U.S. Federal Government in Georgia, Illinois, New York, Tennessee.
- Protection of the habitat, especially of woodland, from urbanization and fires.
- Management of habitat to remove invasive brush in locations where C. acaule is still extant.
- Canopy removal for reproduction and prescribed forest fires.
- Fencing vulnerable sites to protect the species from collection.
- Control and management of the sedative production from the roots.
- Sympathetic management of isolated populations.
- Raising of public awareness.
- Protection of living individuals of the species through legislation and legal protection which ban the species being picked or dug up.
- Ex situ conservation: artificial propagation, re-introduction, seed collections.
- Monitoring and surveillance of the existing populations and sites.
- Estimation of population sizes and study of their dynamics.
Sources: Cribb 1997, Frosch and Cribb 2012, Gupton et al. 1986, Homoya 1993, Kartesz 1994, Luer 1995, Meades et al. 2000, Patrick et al. 1995, Pepoon 1927,and Sheviak 1974.
Relevance to Humans and Ecosystems
Cypripedium acaule is a member of the orchid genus Cypripedium. Members of this genus are commonly referred to as lady's slipper orchids. First described in 1789 by Scottish botanist William Aiton, C. acaule is commonly referred to as the pink lady's slipper, stemless lady's-slipper, or moccasin flower. The pink lady's slipper is the provincial flower of Prince Edward Island, Canada.
Unlike most other members of "Cypripedium", the pouch of C. acaule opens in a slit that runs down the front of the labellum rather than a round opening. The plant consists of two plicate leaves near the ground. From between those leaves sprouts a long, pubescent stalk that bears a single pink flower. The sepals and petals tend to be yellowish-brown to maroon with a large pouch that is usually some shade of pink but can be nearly magenta. The white pouched-green petaled forma alba can occasionally be found mixed in with normal populations.
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Seed germination labs have increased the commercial availability of acaule, although it still tends to be less commonly available than other Cyp species and hybrids. This is primarily due to the extra care that must be provided if the growing site is not naturally suitable for in-ground cultivation. C. acaule grows in soils below a pH of 5, often at 4-4.5. At this high acidity soil fungus is suppressed, and acaule can thrive. There is even evidence that acaule is partially myco-heterotrophic by parasitizing fungus that attempts to invade its roots. However, above pH 5 the soil microbes become more than acaule can manage and the plants rot. Interestingly, seedlings germinated in a sterile environment can grow and thrive in a much higher pH than 5, but must be grown below 5 if removed from the sterility.
For artificial cultivation container culture is a must, and the growing medium must be naturally acidic. Additionally, all other soil additives must be devoid of any calcium that could buffer the pH to above 5. High quality peat moss or pine duff work well, and pH neutral perlite can be added to improve porosity. Due to the risk of calcium bicarbonate, tap water is unsuitable. Rainwater or distilled water mixed with 2ounces of vinegar per gallon will assure that a reliably high acidity is maintained in the growing medium. Give bright dappled shade or morning sun. Sink pots in winter or store in a cold frame for insulation. Given these conditions acaule can thrive indefinitely, but will always require much more maintenance that other species/hybrids that can be grown in a wider pH range.
Cypripedium acaule can be found in the eastern third of the United States, particularly in the Great Lakes Region and the Northeast, south along the Appalachians to Alabama. It also widespread in Canada, found in every province except British Columbia. It also occurs in the Northwest Territories and in St. Pierre & Miquelon. This widespread species can be found in a wide variety of environments, from coastal plains, to pine barrens, to mountaintops.
C. acaule requires highly acidic soil but tolerates a range of shade and moisture, though it prefers at least partial shade and well-drained slopes. It is usually found in pine forests, where it can be seen in large colonies, but it also grows in deciduous woods. It was long speculated that a fungus association was needed for growth, and that acaule could not be artificially cultivated outside of these associations. However, a greater understanding of orchids in general has shown that this association is only needed to germinate orchid seeds, and is not required once plants begin making true leaves.
This species is common in parts of the northern United States and adjoining provinces of Canada, but it is considered endangered in Illinois and Tennessee, Vulnerable in New York, and Unusual in Georgia.
- "Cypripedium acaule". NatureServe Explorer. NatureServe. Retrieved 2008-04-27.
- Voitk, A & M. (2006) Orchids on the Rock: The Orchids of Newfoundland, Rocky Harbour, NL: Gros Morne Co-operating Association.
- Cribb, Phillip, and Green, Peter. The Genus Cypripedium Kew Royal Botanic Gardens, Timber Press 1997. ISBN 0-88192-403-2
- Dickinson, T.; Metsger, D.; Bull, J.; & Dickinson, R. (2004) ROM Field Guide to Wildflowers of Ontario, Royal Ontario Museum, Toronto:McClelland and Stewart Ltd., p 89.
- Provincial Flower, PEI
- USDA Plants Profile
- Biota of North America Program, county distribution map
- Cribb, P. & Bailes, C. Hardy Orchids. Orchids for the Garden and Frost-free Greenhouse. London:Christopher Helm, 1989. ISBN 0-7470-0416-1
- Cypripedium acaule, moccasin flower, USDA