There is just as much learning, or more, going on at my end of this blog as there is at the readers’. A Vermont naturalist recently sent me a photograph of an upside down Pink Lady’s Slipper (Cypripedium acaule). Over 50 years in the field and I have never come across this phenomenon, nor was I familiar with the process that produced it.
Some flowers, including many orchids, are “resupinate.” While the flower is developing, the flower stalk does a 180 degree twist, bringing what would be the bottom of the flower to the top. With lady’s slippers, the labellum, or lip, is inverted, so that it ends up not above the other two petals, but below them. This modified petal, or pouch, serves to attract pollinating insects and acts as a landing platform for them. For some unknown reason, the stalks of the pictured Pink Lady’s Slippers never twisted, allowing us to see the original position of the labellum in both flowers. (Photo by Sue Wetmore)
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As with Pink and Yellow Lady’s Slippers, one of Showy Lady’s Slipper’s three petals is greatly modified into a large inflated pouch called the labellum. The two other petals attract pollinators with an alluring odor, but the insects that enter into this pouch are in for a disappointment, as lady’s slippers produce little or no nectar. Once inside, visiting insects are guided by very fine, slanting hairs on the inner surface of the pouch towards the flower’s pistil and stamens. Once it has entered the constricted passageway that leads to the reproductive parts, an insect cannot turn around and must pass by the pistil and stamens. Lady’s slippers rarely self-pollinate, so it is crucial that they not only attract, but also extract pollen from insects to achieve cross-pollination. Thanks to their structure, this happens more often than not. The flowering of Showy Lady’s Slippers peaks in Mid-June in central Vermont; if you know of a nearby fen (peat wetland that gets its water from rainfall and surface water), best visit it soon, as that’s where you’re most likely to find this species of orchid.
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Pink Lady’s Slippers (Cypripedium acaule), also known as Moccasin Flowers, differ from Yellow and Showy Lady’s Slippers in two fairly obvious ways. One is that the stalk the single flower is borne on bears no leaves. In addition, the pouch, or labellum, has a vertical slit running the length of it, rather than an oval opening on the top. Bumblebees are the only insect strong enough to push their way through this slit and are their main pollinators. In New England, almost 25% of the Pink Lady’s Slipper population have white flowers (see insert).