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.
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.
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.
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.