Herbs, perennial. Roots closely to widely spaced along rhizome, slender, fleshy; rhizomes short to elongate. Stems leafy or scapose. Leaves alternate, in single radical pair, or subopposite near midpoint of stem, ascending to spreading, plicate, bases sheathing stem. Inflorescences terminal, solitary; flowers solitary or 2–several in lax racemose spike; bracts large, foliaceous. Flowers resupinate, showy; sepals distinct or lateral sepals usually connate proximal to lip forming synsepal; petals entire; lip inflated, slipper- or sac-shaped, with adaxial orifice; pollinaria absent; loose granular pollen in 2 lateral anthers, dorsal anther a large subapical staminode; stigma free, 2–3-lobed. Fruits capsules, ellipsoid to oblong-ellipsoid.

Distribution

Primarily temperate Eurasia and North America, ranging from arctic to subtropics in East Asia and Cordilleran North America and Central America.

Discussion

Species ca. 45 (12 in the flora).

Selected References

Cribb, P. J. 1997. The Genus Cypripedium. Portland.

Sheviak, C. J. 1992. Natural hybridization between Cypripedium montanum and its yellow-lipped relatives. Amer. Orchid Soc. Bull. 61: 546–559.

Lower Taxa

Cypripedium acaule, Cypripedium arietinum, Cypripedium californicum, Cypripedium candidum, Cypripedium fasciculatum, Cypripedium guttatum, Cypripedium kentuckiense, Cypripedium montanum, Cypripedium parviflorum, Cypripedium passerinum, Cypripedium reginae, Cypripedium yatabeanum

Key

1	Lip orifice a longitudinal fissure, length of lip; leaves 2, radical, stem a leafless scape.	Cypripedium acaule
1	Lip orifice basal, 4–37 mm; leaves 2–several, cauline.	> 2
2	Lip appearing angular, adaxial surface swollen near middle, apex abruptly deflected downward; lateral sepals distinct.	Cypripedium arietinum
2	Lip not angular, slender slipper-shaped to globose sac, apex not deflected; lateral sepals connate or nearly distinct.	> 3
3	Leaves 2, subopposite to alternate, near midpoint of stem (very rarely, leaves 3, closely alternate near midpoint of stem); lip prominently marked reddish or brownish between veins.	> 4
3	Leaves 3 or more (very rarely 2), alternate on basal to middle portion of stem or along length; lip yellow, ivory, or white, without extensive markings between veins.	> 6
4	Flowers (1–)2–4 in short nodding spike, dull yellow to reddish brown or dark purple, lip mostly 8–14(–25) mm.	Cypripedium fasciculatum
4	Flowers solitary, erect, white to yellowish or greenish, mottled with pink or brownish; lip 15–30 mm.	> 5
5	Petals slightly shorter than to equaling globose to obovate lip, constricted near apex, lanceolate-subpandurate in general outline; markings pink to magenta.	Cypripedium guttatum
5	Petals much shorter than oblance-fusiform to oblance-ovate lip, constricted near middle, acuminate-subpandurate to pandurate in general outline; markings brownish or tan.	Cypripedium yatabeanum
6	Petals flat, oblong to ovate, unmarked, white or green, yellow-green, or brownish.	> 7
6	Petals spirally twisted or undulate (rarely flat), linear-lanceolate, or rarely linear-oblong, spotted and striped (sometimes minutely so) or suffused with darker reddish brown or madder on yellowish or greenish ground color (rarely without markings).	> 9
7	Flowers large; lip 25–53 mm.	Cypripedium reginae
7	Flowers small; lip 11–20 mm.	> 8
8	Plants usually less than 35 cm; flowers 1(–2); lateral sepals nearly distinct to connate almost to apex.	Cypripedium passerinum
8	Plants usually much more than 35 cm; flowers 3–18(–22); lateral sepals connate almost to apex.	Cypripedium californicum
9	Lip orifice 27–37 mm; flowers very large; lip (41–)53–65 mm, ivory to pale yellow.	Cypripedium kentuckiense
9	Lip orifice usually less than 23 mm (rarely to 27 mm, then lip deep yellow); flowers smaller; lip mostly 15–45 mm (rarely to 54 mm, then lip deep yellow), white or yellow.	> 10
10	Lip white, rarely suffused with magenta; staminode lanceoloid or oblong-lanceoloid to ellipsoid.	> 11
10	Lip white or yellow; staminode cordiform-ovoid, deltoid to lance-ovoid, or ovoid-oblong (rarely staminode narrower or ellipsoid, then lip yellow).	> 12
11	Sepals and petals green or yellowish, usually spotted and striped with reddish brown or madder; dorsal sepal 15–35 mm; leaves lanceolate or elliptic to oblanceolate, ascending from insertions toward base or middle of stem.	Cypripedium candidum
11	Sepals and petals suffused with reddish brown or madder; dorsal sepal 33–60 mm; leaves suborbiculate to ovate or elliptic-lanceolate, ascending to spreading, inserted toward base or scattered along stem.	Cypripedium montanum
12	Lip white, 19–33 mm; sepals and petals suffused with reddish brown or madder, often intensely so (very rarely clear green), long and slender; dorsal sepal 33–60 mm, ratio of length to width 2.5–6.5; cordilleran.	Cypripedium montanum
12	Lip yellow (very rarely white), 15–54 mm; sepals and petals suffused with reddish brown or madder or more commonly spotted and striped (often minutely so), rarely unmarked, short and broad to long and slender; dorsal sepal 19–80 mm, ratio of length to width 1.3–3.7; widespread.	Cypripedium parviflorum