By Don Lyman
The Boston Globe, May 20, 2021
A pink lady's slipper orchid in the Middlesex Fells Reservation in Stoneham. DON LYMAN
With large, bulb-shaped flowers that range in color from white to various shades of pink, the pink lady’s slipper orchid is one of the most attractive and fascinating wildflowers in Massachusetts.
“They are astonishingly beautiful, with so many unique and strange aspects of biology in this one species,” said Richard Primack, biology professor and plant ecologist at Boston University.
The strange biology of the pink lady’s slipper begins with a tiny seed the size of a dust particle. In fact, all orchid seeds are minuscule and are called “dust seeds,” said Dennis Whigham, senior botanist and founding director of the North American Orchid Conservation Center at the Smithsonian Environmental Research Center in Edgewater, Md.
“Most plants have evolved to put some food into the seed to help the little plant begin to grow once the seed germinates,” Whigham explained. “Orchids have evolved a different strategy. They put their resources into producing thousands of tiny seeds that are wind-dispersed.”
The downside of this reproductive strategy is that the tiny orchid seed has no stored food, so the seed needs to get nutrients from another source. Surprisingly, the source of those nutrients is a fungus called orchid mycorrhiza, said Whigham. Scientists think the fungus enters the orchid seed through a very small opening in the seed wall called a micropyle.
But the fungus-orchid relationship doesn’t end when the seed germinates. Primack said pink lady’s slippers spend their first five years or so as underground bulbs that also are nurtured by the fungus.
Even when the pink lady’s slipper emerges from the soil and grows into an adult plant that is able to photosynthesize and produce carbohydrates that it stores for energy, the orchid appears to derive at least some nutrition from the fungus. There’s still a lot that is unknown, Whigham said, but when the fungus is in the cells of the orchid root, it forms structures called pelotons, which the orchid digests. After the pink lady’s slipper grows into an adult plant, it takes several more years before it flowers, said Primack. In Massachusetts, it blooms from the middle to the end of May.
But lady’s slippers’ flowers aren’t like most other flowers ─ they’re what botanists call “trap flowers,” Primack explained. Bumblebees — the primary pollinators of pink lady’s slippers — are attracted to the flowers, thinking they are going to find food in the form of nectar, like with other flowers. But the bees are deceived ─ there is no nectar. The bee forces its way through an opening in the front of the flower, which closes behind it. The bee is then trapped inside.
There are two escape windows at the top of the flower. On its way out of the flower, the bee encounters a female structure called a stigma, which scrapes pollen off the back of the bee if it has visited a previous flower and has pollen on it. The bee then encounters the anther, a male structure, which produces pollen that is deposited on the bumblebee’s back as it exits.
The majority of orchid flowers are not pollinated, said Primack, who conducted an experimental study on pink lady’s slipper reproduction in the 1980s.
“Bumblebee populations are not that large,” said Primack. “There are not enough naïve bees to pollinate all the flowers [experienced bumblebees will eventually avoid lady’s slipper flowers]. And orchid flowers have to compete with other flowers. Generally, less than 5 percent of the pink lady’s slipper flowers get pollinated.”
If they do get pollinated, the ovary of the flower develops into a fruit, Primack explained. The fruit takes about three months to mature into a capsule the size of a small grape. The capsule contains thousands of tiny dust seeds that shake out from slits in the capsule and get dispersed by wind. If the seeds are lucky enough to land where there’s good growing conditions and if they come in contact with the mycorrhiza fungus, the seeds will germinate and the orchid’s life cycle begins anew. Orchids are the biggest plant family in the world, with an estimated 25,000 plus species worldwide. Most are tropical, said Whigham. There are over 200 orchid species in North America, according to the website, Go Orchids.
Massachusetts has over 50 species of orchids, said Marion Larson, chief of information and education at the Massachusetts Division of Fisheries and Wildlife.
Contrary to popular belief, pink lady’s slippers are not endangered, but there is a law in Massachusetts that limits picking them, said Larson.
Essentially, people may not pick or dig up pink lady’s slippers from any public or private property unless they have written permission from the landowner, Larson said. They may pick them or dig them up only on their own property. Also, people may not buy or sell pink lady’s slippers if there is reason to believe the plants being offered for sale were obtained without landowner permission.
Pink lady’s slippers can live 20 or 30 years, said Primack. Natural threats to the orchids include deer and other herbivores. Pink lady’s slippers are found throughout much of Massachusetts and occur in a wide range of habitats, said Primack, but they don’t like bright sunlight or deep shade. They tend to favor open woodlands and moderate levels of disturbance and are often found near paths.
“Pink lady’s slippers are a remarkably beautiful representative of a large tropical family, and they’re found right here in New England,” said Primack.
Comments