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Cypripedium acaule — pink lady's-slipper

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Facts

Pink lady's-slipper is typically found on acidic soils. It is pollinated by bumblebees that enter the flower through a slit in the labellum, pass under the stigma that removes any pollinium (pollen sac) that may be present on the bee, and then under one of two anthers that attach a pollinium onto the bee. Finally, the bee exits through a small opening in the back of the flower. Contact with the floral bract is known to cause skin irritation in some people; other parts of the plant may also have this effect.

Habitat

Anthropogenic (man-made or disturbed habitats), bogs, forest edges, forests, swamps, woodlands

New England distribution

Adapted from BONAP data

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North America distribution

Adapted from BONAP data

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Characteristics

Habitat
  • terrestrial
  • wetlands
New England state
  • Connecticut
  • Maine
  • Massachusetts
  • New Hampshire
  • Rhode Island
  • Vermont
Leaf arrangement
basal: the leaves are growing only at the base of the plant
Number of leaves on stem
absent
Form of lower petal
the labellum has a pouch-like shape
Lower petal outline
the labellum is simple in form
Main color of lower petal
  • pink to red
  • white
Nectar spur
there are no nectar spurs on the flower
Inflorescence type
the inflorescence has only one flower or a pair of flowers on it
Lower petal characteristics
the labellum is in the shape of a pouch
Lower petal length
30–67 mm
Sepal length
19–52 mm
Show all characteristics

  • Flowers

    Flower petal color
    • brown
    • green
    • red
    • yellow
    Flower symmetry
    there is only one way to evenly divide the flower (the flower is bilaterally symmetrical)
    Flowering date
    • July
    • June
    • May
    Flowers per inflorescence
    At least 1
    Form of lower petal
    the labellum has a pouch-like shape
    Hairs on inflorescence axis
    NA
    Inflorescence type
    the inflorescence has only one flower or a pair of flowers on it
    Labellum position
    the labellum is in the lower position on the flower
    Length of flower stalk
    0 mm
    Length of narrowed base of lower petal
    0 mm
    Length of peduncle
    150–610 mm
    Lobes at base of lower petal
    0 mm
    Lower petal characteristics
    the labellum is in the shape of a pouch
    Lower petal length
    30–67 mm
    Lower petal outline
    the labellum is simple in form
    Lower petal strongly red-veined
    • no
    • yes
    Main color of lower petal
    • pink to red
    • white
    Nectar spur
    there are no nectar spurs on the flower
    Nectar spur length
    0 mm
    Number of stamens
    2
    Orientation of side petals
    the lateral petals slant somewhat downward
    Pollen sacs
    NA
    Self-pollinating flowers
    there are no cleistogamous flowers on this plant
    Sepal length
    19–52 mm
    Sepals fused only to sepals
    the sepals are fused to each other (not other flower parts), at least near their bases
    Shape of viscidium
    NA
    Spots on lower petal
    no
    Spur opening membrane
    NA
    Spur opening shape
    NA

  • Fruits or seeds

    Seed capsule orientation
    the capsule points upwards or is angled outwards

  • Growth form

    Plant green or not
    the plant is chlorophyllous (it has green parts)
    Roots
    the rhizomes do not resemble coral
    Underground organs
    • there are only slender roots on the plant
    • this plant has a rhizome (a horizontal underground stem with roots growing from it)

  • Leaves

    Bract relative length
    the bract is longer than the associated flower
    Features of leaves
    • the leaf does not have any of the mentioned special features
    • the leaf is pleated or folded back and forth along its length
    Leaf arrangement
    basal: the leaves are growing only at the base of the plant
    Leaf blade edges
    the edges of the leaf blade have no teeth
    Leaf blade length
    90–300 mm
    Leaf blade length to width ratio
    2–3.6
    Leaf blade shape
    • the leaf blade is elliptic (widest near the middle and tapering at both ends)
    • the leaf blade is oblong (rectangular but with rounded ends)
    • the leaf blade is obovate (egg-shaped, but with the widest point above the middle of the leaf blade)
    • the leaf blade is ovate (widest below the middle and broadly tapering at both ends)
    Leaf blade tip
    the tip of the leaf blade is obtuse (bluntly pointed)
    Leaf blade width
    25–150 mm
    Leaves during flowering
    there are leaves on the plant when it is flowering
    Number of bracts on stem
    0
    Number of leaves on stem
    absent

  • Place

    Habitat
    • terrestrial
    • wetlands
    New England state
    • Connecticut
    • Maine
    • Massachusetts
    • New Hampshire
    • Rhode Island
    • Vermont
    Specific habitat
    • bogs
    • edges of forests
    • forests
    • man-made or disturbed habitats
    • swamps
    • woodlands

Wetland status

Usually occurs in wetlands, but occasionally in non-wetlands. (Wetland indicator code: FACW)

In New England

Distribution

Connecticut
present
Maine
present
Massachusetts
present
New Hampshire
present
Rhode Island
present
Vermont
present

Conservation status

Exact status definitions can vary from state to state. For details, please check with your state.

Maine
unranked (S-rank: SNR)
Massachusetts
widespread (S-rank: S5)

From Flora Novae Angliae dichotomous key

1.  Cypripedium acaule Ait. N

pink lady’s-slipper. CT, MA, ME, NH, RI, VT. Forests and woodlands, typically on acidic soils.

Native to North America?

Yes

Sometimes confused with

Calypso bulbosa:
labellum with a pair of yellow, apical horns and also with evident, yellow bristles, and plants with a single basal leaf (vs. C. acaule, with the labellum lacking a pair of apical horns and also without evident yellow bristles, and plants with a pair of basal leaves).
Cypripedium arietinum:
plants with 3 or 4 stem leaves, the stems leafy, and labellum with a downward projected point and with an +/- circular opening on the upper side (vs. C. acaule, the plants with a pair of basal leaves, the stems scapose, and labellum without a downward projected point, with a cleft-like opening along its entire upper side).

Family

Orchidaceae

Genus

Cypripedium