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Pink lady’s slipper a species of special concern

Posted Jun 5, 2018 at 2:03 PM

Updated Jun 19, 2018 at 9:37 AM

The pink lady’s slipper (New Hampshire’s state wildflower) is one of the few woodland wildflowers that almost everyone has heard of and gets very excited about seeing. They are blooming right now in woodlands near you.

I was helping out with my school’s senior service day last week. We were cleaning up a campground near Alton Bay. We found large numbers of these showy pink flowers scattered about around the cabins. The students did a great job avoiding trampling them and all seemed aware that they are rare, endangered even, and that it is illegal to pick them. Turns out pink lady’s slippers aren’t rare or endangered, instead they are relatively common. And, in New Hampshire anyway, it isn’t even illegal to pick them (picking is also legal in Maine but is illegal in Massachusetts).

This myth of endangered, off-limits status has been a good thing, it has probably protected the pink lady’s slipper and kept their numbers at a healthy level. However, even though they are common right now, they are listed as a species of special concern because they grow in such a narrow range of soil and climate conditions, don’t transplant easily, don’t propagate from seed easily and really don’t like change at all. This makes their future uncertain given that we live in a time of relatively rapid change.

The obstacles facing the lady’s slipper are enormous. Not counting human impacts (like habitat destruction and over-picking and climate change) there are a variety of natural hurdles a lady’s slipper will encounter as it lives out its long life (some lady’s slippers have been known to reach 100 years of age!).

Germination is the first difficulty a young lady’s slipper must overcome. The pink lady’s slipper (Cypripedium acaule) is a type of orchid. As with most orchids, lady’s slipper seeds have no stored starch, they rely on specific fungi in the soil to germinate and grow. Sometimes seeds wait years for their fungal partners. These fungi crack open the seed and funnel nutrients from the soil to the developing seedling. This symbiotic association between the fungus and the roots of the plant remains in place for the entire life of the lady’s slipper -- one reason they are so difficult to transplant; transplanting tends to disrupt these fungal connections.

Once it has germinated it can be years (10 to 17) before the lady’s slipper first blooms. From then on they don’t bloom every year, most producing seeds only four or five times (this isn’t much for a long-lived plant). In between blooming they’ll remain dormant in the soil, gathering resources until ready to bloom again.

Pollination presents more difficulties. The lady’s slipper sac-like flower is composed of fused petals that form a hollow pouch. The color and fragrance lure bees (bumblebees in particular) inside through a hole in the center of the pouch. Once inside the bees are trapped, the can’t leave the way they came in, instead, they must traverse the length of the flower to exit holes at the top of the pouch. As they crawl through the pouch they brush against the female stigma which collects any pollen the bee happens to be carrying. As the bee exits the flower, the anther (the flower’s male part) deposits pollen onto the bee’s back. For pollination to occur the bee must visit at least a couple lady’s slipper flowers. The problem is, lady’s slippers provide no nectar to reward visiting bees for their efforts, so bees eventually stop coming. As a result, the pollination rate for lady’s slippers is extremely low.

Look around for lady’s slippers. While they are finicky about which fungi they associate with they will grow in a variety of habitats. According to the USDA Forest Service pink lady’s slipper profile, they’ll grow in mixed hardwood - coniferous forest of pine and hemlock or in acidic but well-drained soils under birch and other deciduous trees in our local forests. And, if you find some, take a lesson from my students and try not to disturb them, they have enough to contend with.