Cypripedium acaule

Stemless Lady Slipper

Stemless Lady Slipper, Cypripedium acaule  Little Beartrack Lake, BWCAW, Photo ©1999 by Earl J.S. Rook
Stemless Lady Slipper
Little Beartrack Lake, BWCAW
Photo ©1999 by Earl J.S. Rook

Flora, fauna, earth, and sky...
The natural history of the northwoods


  • Cypripedium, from the Greek, "Aphrodite's shoe", or "Venus' shoe", in reference to the shape of the lip.
  • acaule, from the Greek prefix a (a-), "not, without", and kaulos (kaulos), "plant stem"; hence, "stemless"
  • Stemless Lady Slipper, from
  • Other common names include Moccasin Flower, Pink Moccasin Flower, Pink Lady Slipper


  • Kingdom Plantae
    • Division Magnoliophyta, the Angiosperms (flowering plants)
      • Class Liliopsida, the Monocotyledons 
      • Subclass Liliidae, the Lilies
        • Order Orchidales, the Orchids
          • Family Orchidaceae, the Orchids
            • Genus Cypripedium, a genus of some 30 to 50 species widely distributed across the Northern Hemisphere; 11 in North America and 5 in the North Country.  Among the most primitive, and evolutionarily isolated of all the orchids.
  • Taxonomic Serial Number: 43534
  • Also known as Fissipes acaulis


  • A ¼, ½, ¾, º, é
  • Leaves two, basal, plicate and pubescent;elliptic, 10-25 cm long and (5)8-15 cm wide.
  • Stem terminating a stalk 25 to 40 cm long that arises from between the two leaves
  • Roots arising from a rhizome with a fascicle of fibrous roots.
  • Flower solitary, subtended by a green bract 3-5 cm long by 1-1.5 cm wide.
    • Sepals apparently two (the result of the fusion of the two lateral sepals behind the labellum), lanceolate, 3-5 cm long and 0.5-2 cm wide, purplish-brown to brown, often striped with green.
    • Petals similar in size and appearance to the sepals, 4-6 cm long and 1-1.5 cm wide.
    • Labellum pouch-shaped, inflated, 4-6 cm long by 2.5-4 cm wide, opening by a slit (with inrolled edges) at the front; magenta to whitish-pink, often whitish pink with darker pink venation, rarely all white
    • Stamens
    • Pistils
    • Ovary superior (within blossom) inferior (below flower)
  • Fruit
  • Seed


  • Identifiable as
  • Distinguished from all other North Woods flowers by the brightly colored flower with the distinctive pouch. Distinguished from other Lady Slipper orchids by
  • SIMILAR SPECIES: Cypripedium acaule could probably be confused only with other pinkishCypripedium species such as C. arietinum and C. reginae. However, it is easily separated from these two as they have cauline leaves, whereas the leaves of C. acaule are always basal.
  • Field Marks


  • Alaska to Newfoundland,


  • On acidic substrates under variable conditions of moisture and shade. Often associated with coniferous trees, most typically Eastern White Pine. Especially abundant in partial shade or full sunlight on rocky gneissic or granitic ridges, where it grows in thin dry-mesic to mesic loam, sand and/or pine litter with mosses and lichens. Also fairly common near the edges of swamps, in mixed woods of Trembling Aspen, Red Maple, and White Birch, with or without conifers. Less commonly found in Black Spruce bogs, sometimes in wet sphagnum. Blooming dates range from late May in upland sites to late June in bogs. The pink-flowered form is common and widespread in Muskoka, but the albino form (f. albiflorum) is rare in the District.
  • Cypripedium acaule can be found in two distinct habitat types in Wisconsin: dry, acidic woods, typically on slopes or steep hillsides, and in sphagnum bogs.
  • DISCUSSION: Fuller (1933) noted that C. acaule always grows with its roots in acid soil; root horizon soil pH tested at a number sites in Wisconsin ranged from pH 4-5. He also records that the white-flowered form has been collected in Adams and Rock counties.






  • Sexually by seed
  • FLOWERING DATES: May 20 to July 20, blooming earlier in the southern part of the state and later in the north.
  • POLLINATION: Cypripedium acaule, like the other Cypripediums in Wisconsin, has a deceptive pollination system. Bumblebees are lured into the pouch of the labellum through the slit in the front, attracted by the bright color and sweet scent of the flower. Once inside, they find no reward, and discover that they are trapped--with only one point of escape. Inside the pouch, there are hairs which lead to a pair of openings, one beneath each pollen mass. First, however, the bee must pass under the stigma, so if it bears any pollen from a visit to another flower, it will be deposited before picking up a fresh load, thus preventing self-pollination. Unfortunately, the bees quickly learn from their experiences and soon avoid C. acaule flowers. Thus, like several other orchids in our flora, they are dependent on naive bees, and generally experience very low pollination rates (Davis 1986).
  • Blooms 24 May to 10 July in the North Country.
  • Pollinated by Bumblebees (Bombus spp.)
  • Reproduces by seed


  • Difficult


  • Hardy to USDA Zone 3 (average minimum annual temperature -40ºF)
  • Cultural Requirements
    • Light:
    • Soil:
    • Water:
    • Spacing:
    • Fertilization
  • Size 12"-18"W x 12"-18"H
  • Growth rate
  • Good for
  • Cultivars include
    • variety 'Alba', with
  • Cultivars and species available by mail order from specialty suppliers or at local nurseries



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Last Updated on 21 September, 2002