Cypripedium acaule Ait.

Pink Lady's Slipper

Facts About

Accepted Synonyms: Fissipes hirsuta

Cypripedium acaule, commonly called Pink Lady's Slipper, is widely distributed across the eastern United States and eastern to central Canada, from Alabama to the Northwest Territories. It produces 2 basal leaves and a solitary flower with purplish brown to green petals and sepals. The labellum is a distinctively inflated pouch, magenta to white, often light pink with darker pink venation; a slit with inwardly rolled edges marks the front of the labellum. It is found in forests and woodlands, often near pines or conifers, and occasionally in bogs or swamps.

Cypripedium acaule is considered globally secure, and is common throughout much of its range. It does, however, exhibit persistently low reproductive rates, caused in part by erratic flowering and infrequent pollination. It can be distinguished from other species with similarly pink flowers, such as C. arietinum and C. reginae, by its basal (instead of stem) leaves.

Pollination

This orchid, like most Lady’s Slippers, attracts pollinators through deception. Bees such as Bombus ashtoni, Bombus borealis, Bombus fernaldae, Bombus impatiens, Bombus nevadensis, Bombus pensylvanicus and Bombus vagans are lured into the pouch by the bright color and sweet scent of the flower. Inside, they find no reward but are trapped with a single exit. Hairs lead to a pair of openings, one beneath each pollen mass. As the bee crawls towards the opening, it rubs against the stigma and any pollen it is carrying pollinates the flower. Finally, as it squeezes out of the flower, new pollen is pressed on to the bee to be carried to the next plant. Bees quickly learn from this experience and soon avoid these flowers which accounts for low pollination rates for this orchid.

Ecosystem Type

Bogs, forests, swamps, woodlands

Characteristics

Habitat:
terrestrial
Leaf arrangement:
basal
Number of leaves on stem:
absent
Form of the labellum:
the labellum is pouch-like
Labellum outline:
the labellum is simple
Main color of labellum:
  • pink to red
  • white
Nectar spur:
absent
Inflorescence type:
the inflorescence has one flower or a pair of flowers
Labellum characteristics:
the labellum is saccate
Labellum length:
30–67 mm
Sepal length:
19–52 mm
Plant height:
10–61 cm
Show All Characteristics

Native to North America

Yes

North American Conservation Status & Distribution

Conservation Status

Select a location to view conservation status:

Conservation and Wetland Status
Global Rank Secure
US Status N/A
Canadian Status Secure

North America Distribution

Adapted from USDA data