Love ‘Em and Leave ‘Em

I am always pleasantly surprised, when tromping through the woods, to come upon Pink Lady’s Slipper (Cypripedium acaule) in full flower. I have fond memories exploring the Pitch Pine (Pinus rigida) woods as a boy behind my grandparents’ backyard on Cape Cod. Large stands of Pink Lady’s Slippers grew in the duff under the pines. They are in flower now and I recently found about 20 plants growing in a stand of mature White Pine (Pinus strobus). This species likes the acidic soils under conifer stands.

The Lady’s Slipper flower on the left shows the slit in the labellum that bumblebees will squeeze into to try to find nectar. It is like a lobster trap in that they can’t exit the same way they came in. Notice the duff, the decomposing pine needles that the plant is growing in. Photo by the author.

I was surprised too that these plants had not been gobbled up by the White-tailed Deer (Odocoileus virginianus) that now overpopulate Connecticut’s forests. This must be because the plants were just off a hiking trail used by lots of people who walk their dogs there. The dogs’ marking activities filled the area with a “predator” scent.

Pink Lady’s Slippers are members of the second largest plant family: the Orchidaceae. Although fairly common, Pink Lady’s Slippers are declining in many areas from habitat loss, careless overcollecting, and browsing by deer. Deer eat native plants like these orchids and leave unpalatable non-native, invasive plants. It is not the fault of the deer, but ours. Our grassy yards interspersed among patchy woods have created the perfect edge habitat for deer. Most of Connecticut’s other orchid species are also much more threatened by these factors.

A Pink Lady’s Slipper depends on bumblebees to pollinate it. The bumblebees are attracted by the color of the flower, hoping to find nectar. But it is a trick—there is no nectar. The bees enter a small slit in the labellum, the modified petals that form the “slipper” (which gives rise to its other name, “Moccasin Flower”). Once inside, the bee crawls under an anther that attaches a sticky pollinium, or pollen sac, to the bee’s back. When the bee flies to another Pink Lady’s Slipper to try again, it passes under the stigma, which removes the pollinium and fertilization then takes place. The bee leaves through a small opening in the back of the flower. As in most members of this plant family, the pollinated flower forms a capsule that then dries and splits open, releasing lots of very tiny seeds.

Because bumblebees often don’t visit another Lady’s Slipper flower after not getting a nectar reward, successful pollination rates are rather low. If successfully pollinated, the plant will form a capsule filled with small seeds. Photo by Susan Elliott, CC BY 4.0 <https://creativecommons.org/licenses/by/4.0&gt;, via Wikimedia Commons.

The tiny Pink Lady’s Slipper seeds do not store any food, so they need to interact with a Rhizoctonia fungus in the soil to survive. The fungus gives the seed nutrients for germination and growth. As the plant grows larger, the fungus will in turn get nutrients from the orchid’s roots. This is a symbiotic relationship that has evolved over millennia in which both species benefit.

Pink Lady’s Slipper seeds are tiny! Photo by Charles de Mille-Isles from Mille-Isles, Canada, CC BY 2.0 <https://creativecommons.org/licenses/by/2.0&gt;, via Wikimedia Commons.

It is this relationship with fungi and the need for acidic soil that dooms this orchid when people dig up Pink Lady’s Slippers from the wild and try to transplant them to their yards. It is best to enjoy these stunning flowers where they live, take a photo, and leave with a happy memory.

Published by Jim Sirch

Jim Sirch is the author of Beyond Your Back Door, a weekly blog about nature in your neighborhood. He is also Education Coordinator for the Yale Peabody Museum, a UConn Master Gardener and board member of his local land trust. As a trained naturalist, he brings a deep understanding of geology, plants and wildlife and how they interact within a particular ecosystem. He holds a B.S in Forestry from West Virginia University, a B.S. from Miami University in Science Education; and an M.S. in Environmental Studies Administration from Antioch University. He is also the 2014 Sigmund Abeles Award recipient from the Connecticut Science Teachers and Supervisors Association for outstanding science teaching and professional development.

5 thoughts on “Love ‘Em and Leave ‘Em

  1. There is a wonderful bunch of them on a hill in Chatfield Hollow State Park- It’s so wonderful to round a corner and see these pink wonders! Thanks for a more in-depth understanding of them.

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  2. Thanks for your informative post! That is interesting about the deer eating them. Would the deer eat the entire plant, leaves and all? My friends and I just completed our 3rd annual ladyslipper counting hikes (two different hikes) and we noticed noticed that 2020’s count was much higher compared to 2019 and 2021 (for example, for one of our hikes the numbers were 2019 = 400; 2020 = 540; and 2021 = 415). Granted it is not super formal (although we do use a clicker) — just what we can see from the trail – so I am wondering if you can shed any light on changes from year to year that might cause different yields. By the way, we don’t discriminate between flowering plants vs. just the leaves. I would be very curious to hear your insights!

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    1. Hi Renee, that’s interesting that you are counting them. Deer will eat flowers and leaves, which can kill the plant since it is no longer able to photosynthesize. Best, Jim

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