Rams-head lady's-slipper (Cypripedium arietinum)

Rams-head lady's-slipper in flower
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Rams-head lady's-slipper fact file

Rams-head lady's-slipper description

GenusCypripedium (1)

Growing to a maximum height of just 30 centimetres, the rams-head lady’s-slipper (Cypripedium arietinum) is an easily overlooked orchid. Yet this species is much appreciated for its beauty and for its pleasant, delicate fragrance (2). It is also one of the most distinctive of the lady’s-slipper orchids (Cypripedioidea), with its small, terminal flower bearing a pouched lower lip that is shaped like an inverted conical hat and covered in a crimson net-like pattern and dense, white hairs (2) (3) (4)

The flower of the rams-head lady’s-slipper has purple to brownish sepals, which are often streaked with green. The outermost sepals are divided all the way to the base and are similar in size and shape to the petals (3). The bluish-green leaves of the rams-head lady’s slipper emerge along the stem in a spiral arrangement (5).

Also known as
ram’s head, ram’s-head lady’s slipper, ram’s-head orchid.
Height: 8 - 30 cm (2)

Rams-head lady's-slipper biology

The rams-head lady’s-slipper is a long-lived plant that reaches maturity at 10 to 16 years, but potentially lives many years longer. Flowering occurs from mid-May to mid-June, when this species is pollinated by small and mid-sized bees, which are attracted to the plant by a sweet odour emitted from the sepals, petals and lower lip of the flower. Not every individual plant flowers each year, with some only flowering in alternate years (2) (5)

Once the flower is fertilised, the upper sepal lowers over the opening of the pouched lower lip to exclude additional insects. The seeds of the rams-head lady’s-slipper are tiny and may be dispersed widely by wind, water or animals. However, germination only occurs when the seeds are in the presence of a compatible fungal partner with which the roots of the rams-head lady’s-slipper have a symbiotic relationship (2).


Rams-head lady's-slipper range

The rams-head lady’s slipper is native to east-central North America, where it is concentrated in the Great Lakes-Saint Lawrence region (2). Its range extends from Saskatchewan to Quebec, Canada, south to Minnesota, Wisconsin, and Michigan, and east to Massachusetts, Connecticut, New York, Maine, New Hampshire, Vermont, U.S., and Nova Scotia, Canada (5).


Rams-head lady's-slipper habitat

The habitat preferences of the rams-head lady’s-slipper vary rather considerably across its range. However, it generally grows in cool, moist, loose, slightly acidic or neutral soils in woodlands, coniferous forests or open stands of cedar (4) (6). It also grows in shady roadside ditches (4), and reaches its largest size in swamps or bogs (2).


Rams-head lady's-slipper status

This species has yet to be classified by the IUCN.


Rams-head lady's-slipper threats

The greatest threats to the rams-head lady’s slipper are habitat alteration, habitat destruction, and over-collection by orchid enthusiasts (5)

While light selective harvesting of forests may actually benefit the rams-head lady’s-slipper, modern clear-cutting using heavy equipment can subject this species to increased light intensity and changes in soil moisture, to which it is intolerant (2) (5). Such activities may also alter the diversity of soil microorganisms, including the fungi that form beneficial associations with this orchid’s roots. In the Great Lakes region, increasing shoreline development and recreation pressures also threaten the habitat of the rams-head lady’s slipper’s (5)

Orchids are popular among speciality gardeners, and populations of the rams-head lady’s slipper are vulnerable to over-harvesting by unscrupulous collectors. Plants taken from the wild rarely survive, and since it has never been successfully propagated, plants for sale have certainly been taken from the wild (6)

In addition, some populations of the rams-head lady’s slipper in Nova Scotia, Canada, have been lost to gypsum mining and cattle grazing (2).


Rams-head lady's-slipper conservation

Conservation efforts directed at the rams-head lady’s slipper should involve protecting its habitat in areas where habitat loss is likely, such as around the Great Lakes, in areas of development, and where clear-cutting takes place. Education strategies and strict enforcement of legislation should also be used to minimise illegal collecting of this species (5).


Find out more

Find out more about the rams-head lady’s-slipper:



This information is awaiting authentication by a species expert, and will be updated as soon as possible. If you are able to help please contact:



The fusion of gametes (male and female reproductive cells) to produce an embryo, which grows into a new individual.
Fungi are one of the taxonomic kingdoms, separate from plants and animals. They obtain nutrients by absorbing organic compounds from the surrounding environment.
The beginning of growth, usually following a period of dormancy and in response to favourable conditions. For example, the sprouting of a seedling from a seed.
To transfer pollen grains from the stamen (male part of a flower) to the stigma (female part of a flower) of a flowering plant. This usually leads to fertilisation, the development of seeds and, eventually, a new plant.
A leaf-like, usually green part of the protective outer layer of a flower bud.
Symbiotic relationship
Relationship in which two organisms form a close association. The term is now usually used only for associations that benefit both organisms (a mutualism).


  1. ITIS (April, 2011)
  2. Blaney, S. and Mazerolle, D. (2007) Nova ScotiaProvincial Status Report on Ram’s-Head Lady Slipper (Cypripedium arietinum R. Br.). Nova Scotia Department of Natural Resources, Nova Scotia. Available at:
  3. University of Wisconsin-Madison Department of Botany - Cypripedium arietinum (July, 2011)
  4. U.S. Forest Service - Cypripedium arietinum (July, 2011)
  5. Michigan Natural Feature Inventory - Cypripedium arietinum (July, 2011)
  6. Maine Natural Areas Program - Ram’s-head lady’s-slipper (July, 2011)

Image credit

Rams-head lady's-slipper in flower  
Rams-head lady's-slipper in flower

© Tom Nelson

Tom Nelson
57 Park Terrace E. #B 49
New York
United States of America
Tel: +1 (212) 567-3143


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