This section is from "The American Cyclopaedia", by George Ripley And Charles A. Dana. Also available from Amazon: The New American Cyclopędia. 16 volumes complete..
Lady's Slipper, the common name, corresponding to the generic one, of orchidaceous plants of the genus cypripedium (Gr.kύπρις , a name of Venus, and πόδδιον, a sock), also sometimes called moccason flower. The genus and two other allied ones differ from other orchids in having two anthers instead of one; the sepals are three, two of them frequently united; petals three, of which the lower one, or lip as it is termed in orchids, is inflated to form a large sac, which in some species bears a resemblance to a slipper. To add to the ordinarily strange appearance of the flower, the lateral petals are in some of the exotics prolonged to form tails, which hang down for several inches below the lip. The genus has a wide range, from the tropics, where they have leathery and persistent leaves, to Canada and Siberia; the leaves of the northern ones are thin, and perish with the stem after flowering. Our commonest native lady's slipper is the stemless (C. acaule), which is found in woods, especially under evergreens, from the Caroli-nas to Canada, but is much more frequent northward; it has two large oblong leaves, from between which arises a stem, sometimes a foot high, bearing at its summit a single large flower, the lip of which, about 2 in. long, is beautifully veined with rose purple on a lighter or white ground.
Two yellow-flowered species (C. parviflorum and C. pudescens), which differ but little except in size, are not rare in bogs and woods; these have leafy stems 1 to 2 ft. high, and one to three flowers. The roots of these are used by herb doctors as antispasmodics under the name of nervine, nerve-root, etc. The ram's-head and small white lady's slipper (C. arietinum and C. candidum) are the rarest of our native species, and highly prized by botanists. The most beautiful of the American, and in some respects the finest of all cy-pripediums, is the showy lady's slipper (C. spectabile); though not very common, it grows in abundance in cold bogs in some localities upon the northern border, and extends along the mountains as far south as North Carolina. The stems, about 2 ft. high, as well as the numerous ovate leaves, are downy, and bear at the summit one to three large flowers, of which the much inflated lip is white, and marked in front with pinkish purple, the color shading off much after the manner of the cheek of a well ripened peach.
This species, so highly prized abroad, is seldom seen in cultivation in its native country; there is nothing in the whole range of hardy herbaceous plants that equals it in beauty, and it may be cultivated by any one who will imitate its natural locality by preparing a deep peaty soil for it. The same remark as to cultivation applies to all our species. Europe has but a single species, G. calceolus, which has a yellow lip netted with purple veins. The tropical and sub-tropical species and varieties of the greenhouse and stove are numerous; the best known of these is C. insigne, from Nepaul, which has thick dark green leaves, and flowers spotted and mottled with yellow, green, and purple. An old plant of this forms a large clump with numerous flowers, which keep in perfection for several weeks; it is well suited to the greenhouse or conservatory, as is the somewhat similar G. venustum, which has broader and spotted leaves.
Lady's Slipper (Cypripedium spectabile).
Nepaul Lady's Slipper (Cypripedium iusigne).
 
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