Polemonium lacustre

Rose and Sytsma (2023) elevate Polemonium occidentale ssp. lacustre to the full species as P. lacustre.

This perennial herb occurs in the Great Lakes Region of the north central USA in Minnesota (St. Louis and Itasca Counties) and Wisconsin (Florence County) where there are five extant populations. Although a great deal of potential habitat exists and known populations are viable with potentially 1,000's plants, the number of individual genets is not known and extensive surveys have not turned up more locations. Further research into the life history and biology including pollinators and seed dispersal mechanisms may explain what is limiting the expansion of this species. Information on total population size as well as response to climate change may change the status.

Polemonium occidentale ssp. lacustre occurs in St. Louis and Itasca Counties in Minnesota and Florence County in Wisconsin (Carlson and Sather 2003, NatureServe Network Element Occurrence Data 2014, MN DNR 2024, WDNR 2024).

There are two element occurrences in Wisconsin, one of which has not been relocated in recent surveys and four element occurrences in Minnesota. A fifth historic element occurrence in Minnesota, documented in 1946, remains unverified. Wherry (1945) referred to a possible historical collection from Michigan. Though there was much searching in Minnesota and Wisconsin during 1992 94, many reasonable habitats have not been searched, and vegetative plants in small patches could easily be missed.

There are a number of threats and practices that have varying degrees of impact to populations, making an overall assessment difficult. As a result, a range was used to address some of this uncertainty. The most likely threats to P. lacustre are changes in the hydrology of habitats; succession and canopy closure; and potentially logging, peat mining, and beaver activity. Beaver activity could flood peatland habitats and convert them to ponds, which would later become sedge meadows (all known sites have had beaver activity, but to date no populations have been flooded). Dewatering of habitat (e.g. associated with road building) could also be a problem in some places. Woody succession may be an important threat because flowering, leaf numbers, and plant vigor are lower with canopy closure. The impacts of logging are unclear. Canopy openings have been shown to increase flowering, but these gains may be short lived. Individuals at MN sites where logging has occurred showed initial increases in number of plants and number of flowering plants. Since then, the population in harvested areas have decreased dramatically (C. Anderson, pers comm.). Although prescribed logging, especially winter logging, or other tree or shrub removal may become an appropriate management measure, unfavorably located slash piles or log landings, insufficiently frozen soil, and some equipment types and operations all could eliminate many plants. All five element occurrences have been logged at some time (two partially cut during 1988-91, one in the 1970's), and all have scattered stumps from earlier logging. Deer herbivory of the cedars may impact habitat favorability by preventing cedar regeneration and changing stand composition (Carlson and Sather 2003, Schmidt 2003, WDNR 2014). Climate change is also a significant threat as it will likely negatively impact habitat quality via increases in droughts and/or flooding.