Cypripedium acaule is a member of the orchid genus Cypripedium. Members of this genus are commonly referred to as lady's slipper orchids. First described in 1789 by Scottish botanist William Aiton, C. acaule is commonly referred to as the pink lady's slipper, stemless lady's-slipper, or moccasin flower. The pink lady's slipper is the provincial flower of Prince Edward Island, Canada and the state wildflower of New Hampshire, United States.
Plants erect, 15–61 cm; stems leafless scapes. Leaves 2, radical, arising directly from rhizome, ascending to spreading; blade broadly elliptic to oblong-, ovate-, or obovate-elliptic, 9–30 × 2.5–15 cm. Flowers solitary; sepals reddish brown to green; dorsal sepal lanceolate to lance-ovate or elliptic, 19–52 × 5–22 mm; lateral sepals connate, synsepal 17–49 × 6–25 mm; petals deflexed to somewhat spreading, somewhat spirally twisted, same color as sepals, linear- to ovate-lanceolate, 24–60 × 4–17 mm; lip magenta to white, obovoid to oblance-ovoid, 30–67 mm, orifice a longitudinal fissure, length of lip; staminode quadrangular to suborbicular-rhomboid or ovoid-deltoid. 2n = 20.