Rare plant spotted for first time in 100 years

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Bridget Rathman, a WDNR Habitat Biologist, and George Riggin, a volunteer with the Rare Plant Monitoring Program, discovered the rare plant outside Cassville, Wisconsin. (Photo courtesy of Jessica Ross)

By Steve Van Kooten


Have you ever searched for a needle in a haystack? How about a thistle in a thicket? A bulb in a bushel?

That’s the sort of thing rare plant monitors do, and George Riggin found his needle near Cassville in 2023.

“It’s one of the most rare plants in the state,” Jessica Ross, the Rare Plant Monitoring Program’s coordinator and WDNR botanist, said. “Riggin has done the most survey work on this plant. He’s the expert.”

Riggin, one of approximately 50 volunteers for the Wisconsin Department of Natural Resources (WDNR) Rare Plant Monitoring program, spent five years rooting around southwest portion of the state in search of Maryland senna (Senna marilandica), a legume that has not been found in Wisconsin in over 100 years.

“This is an important find, just to have this plant in the repertoire of plants that grow in the state of Wisconsin,” Ross said.

According to the Rare Plant Monitoring Program’s 2023 Annual Report, Maryland senna has only been found three times in the state of Wisconsin (1883, 1911 and in the 1970s). Of those three, Riggin determined the most recent population was a misidentification.

In Wisconsin, it’s considered an S1, or very rare. The WDNR has labeled it a species of special concern.

“That says we want to pay attention to those plants because they are rare and may be facing threats within the state. We anticipate and expect numbers to decline in the future,” said Ross. Approximately 15 percent of Wisconsin’s 2,366 native plants are considered rare and are listed as either of special concern, threatened or endangered. “These plants have intrinsic value. We can say they’re pretty, but they also have value to the ecosystem.”

And Maryland Senna isn’t just a pretty face; its yellow flowers, which bloom in July and August, attract pollinators; its beans, which fruit in August and September, serve as a food source for the local wild life; and as a legume, it fixes nitrogen in the soil by taking molecules from the atmosphere and turning them into compounds that can be used by other organisms.

“It’s providing a lot of services for the environment,” said Ross. “Every plan is doing a job in their ecosystem, working in the intricate web.”

Now that the plant has been located, tagged and documented, WDNR ecologists can implement plans to preserve the population. According to the WDNR website, interventions may include prescribed burns and shrub removal to bolster the plant’s chances of survival.

“This population that was around in 1911 is still here now, and we can manage the site so it persists so that we can have it as part of Wisconsin’s flora,” said Ross. “The area was getting overgrown with some aggressive shrubs.”

Nature is not a winner-take-all game. The plants and the animals need each other to survive. While Maryland senna is one of thousands of species, it plays a vital role.

“They’re an important part of this community by sequestering carbon, mediating how water flows across the landscape or providing food for pollinators,” said Ross. “These plants are important in the whole web of nature, and we don’t necessarily know what we’ve lost until they’re gone.”


Rare plant monitors

The Rare Plant Monitoring Program is a volunteer service open to anyone who wants to participate. Plant surveys are conducted in every Wisconsin county, and each one requires different skills, time and effort to complete.

“It’s really a choose-your-own adventure for the volunteers,” said Ross. “People could be slogging through a bog or a swamp and dodging poison sumac, and that’s the most adventurous surveys we have. People could have a survey where they drive up, hop out of their cars, walk to the side of the road and assess how some rare plants are doing.”

Volunteers communicate with professionals and are given locations, descriptions and other information to locate and observe rare plant populations.

For those interested in becoming a rare plant monitor, training can be accessed at https://wiatri.net/inventory/rareplants/volunteer/training.cfm.

For further information, contact Jessica Ross at DNRDLFWPNHRAREPlantMonitoring@wisconsin.gov.

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