This section is from the book "An Illustrated Flora Of The Northern United States, Canada And The British Possessions Vol1", by Nathaniel Lord Britton, Addison Brown. Also available from Amazon: An Illustrated Flora of the Northern United States, Canada and the British Possessions. 3 Volume Set..
Glandular-pubescent herbs, with leafy stems and tufted roots of thick fibres. Leaves large, broad, many-nerved. Flowers solitary or several, drooping, large, showy. Sepals spreading, separate, or 2 of them united under the lip. Lip a large inflated sac. Column declined, bearing a sessile or stalked anther on each side and a dilated petaloid sterile stamen above, which covers the summit of the style. Pollinia granular, without a caudicle or glands. Stigma terminal, broad, obscurely 3-lobed. [Name Greek, Venus' sock or buskin.]
About 20 species, natives of the north temperate zone. Besides the following, some 4 others occur in western North America. Type species: Cypripedium Calceolus L.
Sepals separate; stem leafy, 1-flowered.
Lateral sepals more or less united.
Sepals and petals not longer than the lip.
Plant 6'-10' high; lip about 1/2' long.
Plant 1°-2 1/2° high; lip 1-2' long.
Sepals and petals equalling or longer than the lip.
Sterile stamen lanceolate; lip white.
Sterile stamen triangular; lip yellow.
Stem 8'-12' high, 1-flowered. Leaves 3 or 4, elliptic or lanceolate, 2'~4' long, ¥-3' wide; sepals separate, lanceolate, 8"-10" long, longer than the lip; petals linear, greenish brown, about as long as the sepals; lip 7"-8" long, red and white, veiny, prolonged at the apex into a long blunt spur, somewhat distorted at the upper end which resembles a ram's head, whence the specific name.
Cypripedium passerinum Richards, App. Frank. Journ. 34, 1823.
Stem villous-pubescent, leafy, 6'-10' high, bearing 1 or 2 flowers at the top. Leaves oblong to elliptic-lanceolate, acute; sepals and petals shorter than the lip, the upper sepal broad, nearly orbicular, yellowish; lip nearly spherical, magenta, deeper magenta within toward the base.
Woods and along streams, Ontario to Alberta and the Yukon Territory. Summer.
?C. hirsutum Mill. Gard. Diet. Ed. 8, no. 3. 1768. Cypripedium reginae Walt. Fl. Car. 222. 1788. Cypripedium album Ait. Hort. Kew. 3: 303. 1789. Cypripedium spectabile Salisb. Trans. Linn. Soc. 1: 78. 1791.
Stem stout, villous,-hirsute, 1°-2 1/2° high, leafy to the top. Leaves elliptic, acute, 3'-7' long, 1'-4' wide, flowers 1-3; sepals round-ovate, white, not longer than the lip, the lateral ones united for their whole length; petals somewhat narrower than the sepals, white; lip much inflated, 1'-2' long, white, variegated with crimson and white stripes; stamens cordate-ovate.
Cypripedium candidum Willd. Sp. PI. 4: 142. 1805.
Stem 6'-12' high, leafy. Leaves 3 or 4, elliptic or lanceolate, acute or acuminate, 3'-5' long, 8"-16" wide, with several obtuse sheathing scales below them; bracts 1'-2' long, lanceolate; flower solitary; sepals lanceolate, equalling or longer than the lip, greenish, purple spotted; petals somewhat longer and narrower than the sepals, wavy-twisted, greenish; lip white, striped with purple inside, about 10" long; sterile stamen lanceolate.
C. parviflorum Salisb. Trans. Linn. Soc. 1: 77.
1791. C. pubescens Willd. Sp. Pl. 4: 143. 1805.
Stems leafy, 1°-2 1/2° high. Leaves oval or elliptic, 2'-6' long, 1 1/2'-3' wide, acute or acuminate; sepals ovate-lanceolate, usually longer than the lip, yellowish or greenish, striped with purple; petals narrower, usually twisted; lip much inflated, 8"-2' long, pale yellow with purple lines; its interior with a tuft of white jointed hairs at the top; sterile stamen triangular; stigma thick, somewhat triangular, incurved.
In woods and thickets, Nova Scotia to Ontario and Minnesota, Alabama and Nebraska. Ascends to 4000 ft. in Virginia. Consists of several races, differing mainly in the size of the flowers. Whip-poor-will's shoe. Yellows. Slipper-root. Indian shoe. Yellow moccasin-flower. Noah's-ark. Ducks. American valerian. May-July.