This section is from the book "A Guide To The Poisonous Plants And Weed Seeds Of Canada And The Northern United States", by Robert Boyd Thomson, H. B. Sifton. Also available from Amazon: A guide to the poisonous plants and weed seeds of Canada and the northern United States.
Other Common Names: Moccasin Flower, Cypripe-dium.
The Lady-slippers, since they are among the most beautiful and conspicuous of our native Orchids, are much sought after for decorative purposes.
As early as 1875 Dr. Babcock of Chicago came to the conclusion that annual attacks of skin-poisoning to which he was subject, were due, not, as he had supposed, to Poison Ivy, but to species of Lady-slipper. Since then his suspicion of the plant has been proved correct by other investigators. Dr. McDougal, in 1893, experimented with Cypripedium hirsutum, the Showy Lady-slipper, and found that by brushing it over his arm he produced effects similar to those of Poison Ivy. In fourteen hours his whole arm and hand were much swollen and badly inflamed. The swelling did not go down for ten days, and effects were felt for a month.
Fig. 30. - Showy Lady-slipper - Cypripedium hirsutun.
The poison is in the form of a fatty acid, whose exact composition is not yet determined. It is contained in glandular hairs, which cover the surface of stem and leaves. The effect is strongest in the fruiting period. Even at this time, however, many more people are immune than in the case of Poison Ivy.
The Cypripediums are showy plants with brightly coloured flowers. There are three sepals, coloured like the petals. Two of these are usually united beneath a large, sac-like lip (the "slipper" or "moccasin") formed by one of the petals. The other petals stand out at the sides. There are three stamens, one of which is straplike and sterile. The other two, one on each side, have two-celled anthers with masses of granular pollen. The leaves are many-nerved and plaited, with a sheathing base.
The following species are mentioned as poisonous:
The Smaller Yellow Lady-slipper, Cypripedium parvi-florum Salisb., is a species widely distributed in swampy woods and bogs. Stem six to sixteen inches high; petals and sepals greenish, suffused with madder purple, one to one and a half inches long. Lip yellow with purplish spots or lines.
The Large Yellow Lady-slipper, Cypripedium pubes-cens Willd., somewhat larger and more hairy than the preceding, with a larger lip less strongly marked with purple; often growing in clusters in low woods or on moist prairie.
The Showy Lady-slipper, Cypripedium hirsutum Mill., stem one to two feet high, hirsute, usually in clumps; flowers pink; sepals rounded; lip oblong, much inflated, white marked with crimson; moist woods, Newfoundland to Manitoba and southward.