Cypripedium arietinum Ait. f.

Ram's Head Lady's Slipper

Facts About

Accepted Synonyms: Criosanthes arietina

Cypripedium arietinum, commonly known as Ram's Head Lady's Slipper, has a limited distribution across northeastern and central Canada and the U.S., from Quebec to Wisconsin. It has a distinctively conical and pointed labellum, which is white with reddish veins and covered with thin white hairs. The dorsal sepal curves to form a hood over the labellum, while the lateral petals and sepals, purple or green in color, form spirals which twist away from the pouch. It produces 3 to 5 blueish green leaves on its stems. Although this orchid is known to be pollinated by bees, it primarily reproduces vegetatively through offshoots from its rhizome, sometimes resulting in clusters of over a dozen plants in a single location. It grows in coniferous or mixed forests, swamps, and mossy bogs, often near cedar, spruce, or juniper trees.

Cypripedium arietinum is considered globally vulnerable, and is rare or endangered throughout much of its range.


This orchid is pollinated by female halictid bees such as Lasioglossum coeruleum. The showy white and magenta flowers produce a sweet vanilla fragrance that attracts bees into the pouch formed by the labellum. The bee enter the flower and exits with pollen on its thorax.

Ecosystem Type

Bogs, forests, swamps


Leaf arrangement:
Number of leaves on stem:
  • three
  • four
  • five
Form of the labellum:
the labellum is pouch-like
Labellum outline:
the labellum is simple
Main color of labellum:
Nectar spur:
Inflorescence type:
the inflorescence has one flower or a pair of flowers
Labellum characteristics:
the labellum is saccate
Labellum length:
10–16 mm
Sepal length:
15–25 mm
Plant height:
10–35 cm
Show All Characteristics

Native to North America


North American Conservation Status & Distribution

Conservation Status

Select a location to view conservation status:

Conservation and Wetland Status
Global Rank Vulnerable
US Status N/A
Canadian Status May Be At Risk

North America Distribution

Adapted from USDA data