Picture a carnivorous plant. You’re likely envisioning the giant human-eating Venus flytrap popularized in the 1960 and 1986 remake of the film “Little Shop of Horrors.” While the infamous Venus flytrap only grows naturally in a 70-mile radius area in the Carolinas (and, for the record, doesn’t actually eat humans), there are many other carnivorous plant species that are more widespread — these plants live on every continent except for Antarctica, and several of them abound in the fens and bogs of states of the Midwestern U.S.
In central Wisconsin, one 22-acre parcel of land at the edge of the Central Sand Hills Ecological Landscape is home to a host of unusual flora, including a large population of pitcher plants. The Berlin Fen, which sits next to the town of Berlin, was designated a state natural area in 1986.
Like much of Wisconsin, the geographic characteristics of this area were shaped in large part by glaciers. The rolling horizon of the Central Sand Hills Ecological Landscape is sculpted with terminal moraines — masses of rock and sediment that were left behind at the ends of glaciers, marking their farthest reach. The Berlin Fen State Natural Area and the lands around it have lots of sand and gravel and other deposits that came from these glaciers.
Now, the site is bordered on one side by a road, on the other by an abandoned railroad trail. A meandering stream bisects the parcel.
Berlin Fen actually has two fens, which are a type of wetland ecosystem that takes thousands of years to form and can’t be easily renewed if destroyed. They’re both calcareous mound fens — rare natural communities formed by upwelling groundwater and an accumulation of peat soil, mostly occurring within glaciated areas of southern Wisconsin. Since there is a continual supply of groundwater, the fens are constantly releasing moisture, even in times of drought, according to Jon Robaidek, a Central Sands field ecologist with the Wisconsin Department of Natural Resources (WDNR).
Fens have low oxygen levels because they are constantly wet — conditions that limit decomposition, leading to the accumulation of organic matter like leaves and roots, eventually creating peat soil. Without decomposition, there’s little of the nutrients like nitrogen, potassium and phosphorus that plants usually need to thrive.
But it’s great for carnivorous plants like Sarracenia purpurea — the type of pitcher plant that lives in Berlin Fen — because they evolved to survive in places that lack nutrients. Instead, they get the minerals they need by eating insects.
“These plants can survive where others maybe can’t,” Robaidek said. “That’s why they take advantage of the situation — of their ability to get nutrients through a different method.”
These pitcher plants have purple-veined leaves that are fused along most of their length (creating the “pitcher”) and lined on the inside with downward-pointing hairs. The pitchers collect water, and insects trapped by the hairs die and decay in this pool, providing the plants with minerals.
But these plants also undergo processes that are typical of their non-carnivorous counterparts. They photosynthesize, for one. And they grow wine-red, alien-looking flowers to attract pollinators. The nodding flowers have long stems, which help keep pollinating insects away from the pitchers so they don’t accidentally become a meal.
In Wisconsin, this strategy for survival seems to have worked pretty well. Pitcher plants abound in Berlin Fen, particularly on the larger mound covering the northern part of the site.
“You have to watch where you walk out there,” Robaidek said. “Otherwise, you’re going to step on them.”
And although you might not find too many places where Sarracenia purpurea grows in dense bunches like they do in Berlin Fen, they’re still found across most counties in Wisconsin.
But many habitats home to pitcher plants and other carnivorous plants are under pressure, and the ecosystems that these unusual flora call home are shrinking. Carnivorous plants are particularly vulnerable to ecosystem degradation because they are highly specialized, and their habitats are often very sensitive to disruption.
“Carnivorous plants are really poor competitors,” Joseph Walston, a doctoral student in the University of Wisconsin-Madison’s botany department, said. “Some plants can adapt really quickly to a changing environment, but these carnivorous plants are not good at competing.”
Berlin Fen itself is believed to have survived farm grazing in the past, Robaidek said. Now, there is farming in the upland areas adjacent to the fen. There’s also a landfill and a public trail close by.
Although Berlin Fen is a protected area, the multitude of nearby land uses around the small parcel can strain the environment, particularly by introducing invasive species. Because carnivorous plants aren’t great competitors, invasive species can, according to Wallston, “easily outgrow, outshade [and] outcompete” them, even in a protected state natural area. Robaidek said that much of the WDNR’s time tending to Berlin Fen is occupied with cutting, pulling and treating invasives like cattail, wild parsnip and buckthorn.
But for now, the pitcher plants of Berlin Fen persist. In the summer, you can see their blooming flowers and, gathered below, the veined leaves filled with water, clustered near pools and marl rivulets, making a home where other plants can’t.