Left: Pink Lady's Slipper (Cypripedium acaule). Photo by Grant Fessler.

Illinois is special in being a meeting ground for several of North America's floristic regions. The flora of the Prairie State is comprised of species from the cold boreal north, the moist deciduous forests of the east, the swamps and marshes of the southern coastal plain, and from the plains of the arid west. Accordingly, many species are on the very edge of their range in Illinois and may only persist in specialized habitats. Such is the case for one of the state’s rarest plant species, the Pink Lady’s Slipper (Cypripedium acaule). This mesmerizing orchid typically inhabits acidic, nutrient-poor forests and wetlands in northern and eastern North America, habitats that are exceedingly rare in Illinois. Pink Lady’s Slipper was known historically from a small handful of counties in the northern tier of the state (see BONAP distribution map below), and recently botanists were uncertain if it still existed here since the last time it was documented in Illinois was 1999. However, that changed this year! County-level distribution of Cypripedium acaule in North America. Retrieved from: https://bonap.net/MapGallery/County/Cypripedium%20acaule.png 

In 2024, Plants of Concern expanded into Northwestern Illinois with funding from an anonymous donor and the Illinois Department of Natural Resources. One of the priorities in this first year was to search for threatened and endangered plant species that had not been seen for many years, so, naturally, Cypripedium acaule was at the top of the list.  

Despite several failed attempts to relocate the orchid in years past, I met up with three state biologists to take another look just for the heck of it. Jeff Horn (IDNR District Natural Heritage Biologist), Kaleb Baker (INPC Natural Areas Preservation Specialist), Daniel Pohl (INHS/IDNR Field Forester), and I made our way to the last known location and carefully searched the forest floor. The habitat was dense with brambles and ferns – not the typical sparsely-vegetated environment where I had seen the orchid growing out east. After an hour without any luck, we decided to call it quits and monitor other rare species at the site. “Oh well!” We knew that finding the lady’s slipper was a longshot, and after coming up empty handed, it was easy to believe that it was indeed extirpated. However, as any experienced treasure hunter knows, sometimes you do not find what you are looking for until you give up the search. Not even 15 minutes later, I heard Jeff exclaim “What’s that over there?!” Following the trajectory of his outstretched arm, my eyes landed on a bulbous pink blossom held on a slender stalk above two green basal leaves. In awe, we all gazed down at the beautiful and elusive Cypripedium acaule in perfect bloom.  

With the rediscovery of this population, invasive species removal and prescribed fire can be implemented to aid its survival. In addition, plants in this population have been caged to protect them from deer browsing, a threat that many rare plants are faced with today. It was quite an honor to get to see what might be the last of this species in Illinois, and Plants of Concern is excited to continue collaborating with partners like IDNR to further rare plant conservation. 

From left to right: Jeff Horn, Kaleb Baker, Daniel Pohl, and Grant Fessler. 

Article by Grant Fessler, Plants of Concern Program Coordinator for Northwest Illinois