Cypripedium arietinum

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Cypripedium arietinum
Vulnerable
Vulnerable (NatureServe)[1]
Scientific classification Edit this classification
Kingdom: Plantae
Clade: Embryophytes
Clade: Tracheophytes
Clade: Spermatophytes
Clade: Angiosperms
Clade: Monocots
Order: Asparagales
Family: Orchidaceae
Subfamily: Cypripedioideae
Genus: Cypripedium
Species:
C. arietinum
Binomial name
Cypripedium arietinum
R.Br. (1813)
Synonyms[2]
Synonyms (5)
  • Criosanthes arietina (R. Br.) House (1905)
  • Criosanthes borealis Raf. (1818)
  • Arietinum americanum L.C. Beck (1833)
  • Cypripedium arietinum f. albiflorum House (1923)
  • Cypripedium arietinum f. biflorum P.M.Br. (1995)

Cypripedium arietinum, the ram's head lady's slipper,[3] is a rare terrestrial orchid that grows in lightly to heavily shaded areas with calcareous soils. It is characteristic of the alvars around the Great Lakes in North America].[3][4] In Canada, it is found from Quebec to Saskatchewan, plus an isolated population in Nova Scotia, where it grows on gypsum based soils, 330 km away from the nearest population in Maine.[5][6]

Cypripedium arietinum plants in the wild

Description

Cypripedium arietinum is a herbaceous perennial small lady's slipper growing to 10–40 cm (4–16 in). It typically has 3, but sometimes 4–5, leaves and normally has a single flower per flowering stem but in the form biflorum there may be two flowers per stem.[7] The purplish-red flower has light venation and is white at the lip. The flower has three petals, one modified into a densely hairy pouch with white and purplish markings. The sepals are green with reddish-brown markings and the side sepals are to some degree spirally twisted, linear to linear-lanceolate in shape, and are free, in contrast to other North American species in this genus.[8] The other sepal is broadly elliptic to ovate-lanceolate in shape. It flowers in May and June. The diploid (2n) chromosome count is 20.[7]

Taxonomy

The botanist Robert Brown formally described Cypripedium arietinum in 1813, noting that the plant had been introduced to the Kew Gardens in 1808 by horticulturalists Chandler and Buckingham.[9][10] The species epithet arietinum means "ram-like" in Latin. This, and the common name ram's-head lady slipper, make reference to the shape of the flower, which resembles a ram's head.[11]

In 1818, Rafinesque proposed that "Cypripedium arietinum must form a peculiar genus," and placed in a new genus Criosanthes, giving it the name Criosanthes borealis.[12] House supported the recognition of Criosanthes as a monotypic genus but recombined the species as Criosanthes arietinum in 1905.[13] Beck also rejected the plant's placement in Cypripedium, "as it is so very different from all the species of that genus," and placed it in another new, monotypic genus, giving it the name Arietinum americanum.[11]

Modern authorities, including the Flora of North America and Plants of the World Online accept the placement of this species in the genus Cypripedium.[14][10] In his 1997 monograph of Cypripedium, Phillip Cribb recognized taxonomic sections composed of closely-related species, placing C. arietinum and C. plectrochilum (native to east Asia) together in Cypripedium sect. Arietinum. A 2011 phylogenetic analysis using nuclear ribosomal ITS sequences and chloroplast sequences supported the hypothesis that these two species form a monophyletic group.[15] Further phylogenetic work in 2024 suggested that Arietinum was one of the earliest-diverging sections in the evolution of Cypripedium, splitting from most other lineages in the early Miocene, 20.6–12.15 million years ago.[16]

In 1923, House described a form of the plant with green sepals and petals and white lips as Cypripedium arietinum f. albiflorum.[17][18] However, modern taxonomic treatments do not recognize this color variant as taxonomically meaningful and do not recognize forma albiflorum.[18]

Distribution and habitat

While populations of Cypripedium arietinum are declining elsewhere in eastern North America, the orchid flourishes abundantly in Anticosti Island, making the island a refuge for this plant.[19]

Cypripedium arietinum is a forest understory species, it occurs in coniferous to mixed forests and in bogs dominated by Thuja occidentalis (northern white cedar), Larix laricina (tamarack), or Picea mariana (black spruce) where it grows on small mounds produced by Sphagnum mosses.[8] In Minnesota, it more commonly occurs in upland forests dominated by coniferous tree species such as Pinus resinosa (red pine) or Pinus banksiana (jack pine) in weakly acidic (or nearly neutral) soils composed of either loam or clay, it is also found in sandy soils.[8] In northern New England, it often is found in mixed hardwood and softwood forests. [20]

Ecology

Cypripedium arietinum spreads primarily by producing offshoots, sometimes forming large clumps of genetically identical plants. The flowers are not self-fertile, meaning that sexual reproduction requires outcrossing, accomplished when pollinators carry pollen from one flower to another. The only known pollinators are sweat bees in the subgenus Dialictus, including Lasioglossum coeruleum, which are attracted to the flower by its fragrance. These bees enter the lip, where pollen is deposited on their dorsal thorax, emerging up to two minutes later.[21]

Within populations of Cypripedium arietinum, the proportion of plants producing seeds in any year is low. As with other orchids, in order to germinate, a seed must develop a mycorrhizal relationship with a currently-unknown species of fungus. The fungus transfers nutrients to the embryo, and the plant may continue to draw nutrients from its fungal associate even after producing photosynthetic shoots.[22]

Herbivory by white-tailed deer significantly impacts the health of Cypripedium arietinum populations, especially in early successional forests where deer are abundant. Heavily-browsed plants do not send up flowering stems the following year, reducing a population's ability to reproduce.[22]

Conservation

Cypripedium arietinum is considered rare to extremely rare in all locations where it occurs.[5] More specifically, it is rare in Ontario[23] and rare in Manitoba. The ram's head lady's slipper is a threatened plant species in other areas within its range, including Wisconsin, Minnesota, Michigan, and Saskatchewan. It is believed to be extirpated in Connecticut. This species is listed as an endangered species in Nova Scotia.[24]

The ram's head lady's slipper is difficult to cultivate and rarely survives transplantation to a garden from the wild. It should never be removed from any natural area.

Conservation efforts of Cypripedium arietinum in New England have been advancing with the optimization of asymbiotic sterile seed germination and sterile seedling cultures. This research is being presented and published in the 2024 World Orchid Conference in Taiwan and in the Orchid Digest. [25]

References

  1. Ames, D., P. B. Acheson, L. Heshka, B. Joyce, J. Neufeld, R. Reeves, E. Reimer, and I. Ward. 2005. Orchids of Manitoba: A field guide. Native Orchid Conservation Inc., Winnipeg.
  2. "Cypripedium arietinum R.Br.: Synonyms | Plants of the World Online | Kew Science". Plants of the World Online. Retrieved 2026-06-30.
  3. NRCS. "Cypripedium arietinum". PLANTS Database. United States Department of Agriculture (USDA). Retrieved 1 July 2016.
  4. Catling, P.M.; Brownell, V.R. (1999). "Alvars of the Great Lakes Region". In Anderson, R. C.; Fralish, J. S.; Baskin, J. M. (eds.). Savannas, Barrens and Rock Outcrop Communities of North America. Cambridge: Cambridge University Press. pp. 375–391. ISBN 9780511574627.
  5. Blaney, S.; Mazerolle, D. (2007). Nova Scotia Provincial Status Report on Ram's-Head Lady Slipper (Cypripredium arietinum R. Br.). Nova Scotia Department of Natural Resources.
  6. Kartesz, John T. (2014). "Cypripedium arietinum". County-level distribution map from the North American Plant Atlas (NAPA). Biota of North America Program (BONAP).
  7. "Cypripedium arietinum in Flora of North America @ efloras.org". www.efloras.org. Retrieved 2020-12-11.
  8. Barbara Coffin; Lee Pfannmuller (1988). Minnesota's Endangered Flora and Fauna. U of Minnesota Press. p. 84. ISBN 978-0-8166-1689-3.
  9. Townsend, William Aiton (1813). Hortus Kewensis, or, A catalogue of the plants cultivated in the Royal Botanic Garden at Kew. Vol. 5. London: Longman, Hurst, Rees, Orme, and Brown. p. 222.
  10. "Cypripedium arietinum R.Br. | Plants of the World Online | Kew Science". Plants of the World Online. Retrieved 2026-07-01.
  11. Beck, Lewis C. (1833). Botany of the Northern and Middle States. Webster and Skinner. p. 352.
  12. The American Monthly Magazine and Critical Review. Vol. 2. February 1818. p. 268.
  13. Bulletin of the Torrey Botanical Club. Vol. 32. New York: The New Era Printing House.
  14. Sheviak, Charles. "Cypripedium arietinum in Flora of North America @ efloras.org". www.efloras.org. Retrieved 2026-07-01.
  15. Li, Ji-hong; Liu, Zhong-jian; Salazar, Gerardo A.; Bernhardt, Peter; Perner, Holger; Tomohisa, Yukawa; Jin, Xiao-hua; Chung, Shih-wen; Luo, Yi-bo (November 2011). "Molecular phylogeny of Cypripedium (Orchidaceae: Cypripedioideae) inferred from multiple nuclear and chloroplast regions". Molecular Phylogenetics and Evolution. 61 (2): 308–320. doi:10.1016/j.ympev.2011.06.006.
  16. Lagou, Loudmila Jelinscaia; Kadereit, Gudrun; Morales-Briones, Diego F (2024-12-16). "Phylogenomic analysis of target enrichment and transcriptome data uncovers rapid radiation and extensive hybridization in the slipper orchid genus Cypripedium". Annals of Botany. 134 (7): 1229–1250. doi:10.1093/aob/mcae161. ISSN 0305-7364. PMC 11688532. PMID 39269134.
  17. Sheviak, Charles J. (1990). "A New Form of Cypripedium montanum Dougl. Ex Lindl". Rhodora. 92 (870): 47–49. ISSN 0035-4902.
  18. "Cypripedium arietinum f. albiflorum House | Plants of the World Online | Kew Science". Plants of the World Online. Retrieved 2026-07-01.
  19. "Cypripedium arietinum Ait. f." North American Orchid Conservation Center. 2011. Retrieved 30 July 2024. ...has a limited distribution across northeastern and central Canada and the U.S., from Quebec to Wisconsin.
  20. Lan Grace, Palifka Nicholas, Sun Ian, Sun Kevin, Anderson Kastner. (2024). Conservation of the Cypripediums of New England. Orchid Digest, Vol. 88-2, Apr., May, June. (in print)
  21. Argue, Charles L. (30 September 2011). The Pollination Biology of North American Orchids: Volume 1 (1 ed.). New York: Springer. pp. 63–66. ISBN 978-1-4614-0592-4.
  22. Brzeskiewicz, Marjory. (2000). Conservation Assessment for Ram's Head Lady Slipper (''Cypripedium arietinum'') unpublished document prepared for the USDA Forest Service
  23. Oldham, M.J.; Brinker, S.R. (2009). Rare Vascular Plants of Ontario (4th ed.). Peterborough, Ontario: Natural Heritage Information Centre, Ontario Ministry of Natural Resources.
  24. "Species at Risk Overview". Nova Scotia Department of Natural Resources. 11 October 2017. Retrieved 15 July 2018.
  25. Lan Grace, Palifka Nicholas, Sun Ian, Sun Kevin, Anderson Kastner. (2024). Conservation of the Cypripediums of New England. Orchid Digest, Vol. 88-2, Apr., May, June. (in print)