Significance of the Report: First collection of Paludella squarrosa in the State of Wisconsin.

Previous Knowledge: Paludella squarrosa (Hedw.) Brid. (Meesiaceae) (Tufted fen moss) is a circumboreal species (CBH 2024; Vitt 2014a). In North America it is relatively abundant in the Rocky Mountains and northern Cascades (Alaska south to northern Washington and Colorado, south and east to Yukon, British Columbia, and southwest Alberta), is spottily distributed throughout the central provinces and territories of Canada (Northwest Territories, Nunavut, Saskatchewan, and Manitoba), and is more abundant around the Great Lakes, Hudson Bay, and eastern Canada. In the United States it has been collected in northern New England (Maine, New York and Vermont), the upper Great Lakes region (Iowa, Michigan, Minnesota, and now Wisconsin), the middle to southern Rocky Mountains (Colorado, Montana, and Wyoming), and in Washington State. Paludella squarrosa is relatively abundant in Iceland and Scandinavia and occurs sporadically throughout the rest of northern Eurasia (Vitt 2014a; CBH 2024; NatureServe 2024).

Discussion: Within Wisconsin, Paludella squarrosa is known only from Oconto County in northeastern Wisconsin at Waupee Lake Swamp Research Natural Area on the Chequamegon-Nicolet National Forest. Paludella was found growing at the northern edge of a mineral-rich, alkaline lake on a floating sedgepeat mat bordering a white cedar swamp (or northern wet-mesic forest) near the main inlet to the lake. Waupee Lake is a calcareous groundwater-fed lake that has an unusually high number of rare and/or threatened, calcium-loving plant species (Janke 1998; Brzeskiewicz 2015; Epstein 2017). Waupee Lake Swamp is at the western edge of the largest wetland complex—including northern wetmesic forest, lowland hardwood forest, alder thicket, northern sedge meadow, marsh communities, and “northern fen”—in the Northeast Sands Ecological Landscape (Epstein 2017).

Three specimens of Paludella squarrosa were collected in the boreal rich fen at Waupee Lake Swamp, either on a floating mat or on peaty soil with the following tracheophytes: Amelanchier arborea (F. Michx.) Fernald, Andromeda glaucophylla Link, Calopogon tuberosus (L.) Britton, Sterns & Poggenb., Campanula aparinoides Pursh, Carex diandra Schrank, Carex lasiocarpa Ehrh., Carex magellanica Lam., Chamaedaphne calyculata (L.) Moench, Comarum palustre L., Cornus canadensis L., Cypripedium acaule Aiton, Cypripedium parviflorum Salisb., Drosera rotundifolia L., Eriophorum viridicarinatum (Engelm.) Fernald, Galium boreale L., Gaultheria hispidula Dombey, Ilex mucronata (L.) M. Powell, Savol. & S. Andrews, Ilex verticillata (L.) A. Gray, Kalmia polifolia Wangenh., Larix laricina (Du Roi) K. Koch, Menyanthes trifoliata L., Osmundastrum cinnamomeum (L.) C. Presl, Picea mariana (Mill.) Britton, Sterns & Poggenb., Platanthera dilatata (Pursh) Lindl. ex L.C. Beck, Rhododendron groenlandicum (Oeder) Kron & Judd, Rubus pubescens Raf., Sarracenia purpurea L., Saxifraga pensylvanica L., Solidago uliginosa Nutt., Thelypteris palustris Schott, Thuja occidentalis L., Toxicodendron vernix (L.) Kuntze, Triglochin maritima L., Typha latifolia L., Vaccinium oxycoccos L., Vaccinium myrtilloides Michx. The tracheophytes were identified in the field but not collected during visits to the site. Appendix 1 lists all the bryophyte species collected in association with Paludella squarrosa at the Waupee Lake site. Of the 23 species of co-occurring bryophytes found at Waupee Lake Swamp, 20 are county records for Oconto County (Freire et al. 2020); this brings the total number of bryophyte species recorded for the county from 128 to 148.

A number of bryophytes present at the site are considered indicator species of moderate-rich to extreme-rich fens, including Calliergon giganteum, Callier-gonella cuspidata, Campylium stellatum, Meesia triquetra, Hamatocaulis vernicosus, Helodium blandovii, Sphagnum warnstorfii, and Tomentypnum nitens; tracheophyte rich fen indicators include Carex diandra Schrank, Platanthera dilatata (Pursh) Lindl. ex L.C. Beck, and Triglochin maritima L. (Chee and Vitt 1998; Vitt and Chee 1990). Crum and Anderson (1981) note the following bryophyte associates of Paludella squarrosa: Campylium stellatum, species of Cinclidium Sw., Drepanocladus trifarius (F. Weber & D. Mohr) Broth., Meesia triquetra, Meesia uliginosa Hedw., Scorpidium scorpioides (Hedw.) Limpr., and Sphagnum warnstorfii. Of these associates, only Campylium stellatum, Meesia triquetra, and Sphagnum warnstorfii have been located at Waupee Lake Swamp; Drepanocladus trifarius, Meesia uliginosa, and Scorpidium scorpioides are known from other rich fen sites in Wisconsin.

Ongoing searches in Wisconsin for Paludella squarrosa since 2021 have not yielded additional occurrences, despite repeated visits to other sites considered suitable (Epstein 2017; S. Janke, personal communication; K. Doyle, personal communication). In Wisconsin, boreal rich fen is most common along the Door Peninsula (northeastern Wisconsin), with a few additional recognized sites on the “mainland” of the state, mainly in northeastern Wisconsin (Epstein 2017). Paludella squarrosa is apparently quite rare in Wisconsin, although suitable habitat appears to be present in the state. According to Chee and Vitt (1990), Paludella is known from intermediate to extreme-rich fens, though Vitt (2014b) indicates that the species is restricted to extreme-rich fens. Though Wisconsin has other rich fen sites with several rich fen indicator species, perhaps the conditions are rarely sufficient for Paludella to thrive.

A review of herbarium records of Paludella squarrosa in the Upper Great Lakes region shows that ca. 39 vouchered specimens have been collected from approximately 26 locations in Ontario, Canada (most recently in 2013); nine vouchered specimens have been collected from approximately eight locations in three counties in Minnesota (most recently in 1984); and ca. 17 vouchered specimens have been collected from approximately ten locations in three counties in Michigan (most recently in 1974) (CBH 2024). A search of iNaturalist (2024) records from the western Great Lakes region shows six observations from Ontario, Canada, three from the single known Wisconsin site, one observation from the Lower Peninsula of Michigan, and no further observations from Minnesota. Paludella squarrosa is found in calcareous wet fens in North America and Eurasia (Vitt 2014a, Jenkins 2020) and has an obligate wetland indicator status (Gillrich and Bowman 2010). Specific habitat for P. squarrosa has been described as wet calcareous substrates and fens in Maine (Ledlie and Allen 2019), calcareous fens in Minnesota (Leete et al. 2016), bogs and bog margins in Michigan (Mazzer and Sharp 1963), montane calcareous fens in Montana (Elliot and Pipp 2020), rich graminoid fens in New York (Slack 1992), mineral-rich fens in Vermont (Thompson et al. 2019) and montane flow-through fens dominated by graminoids in Wyoming (Heidel and Jones 2006).

Diagnostic Characters: Paludella squarrosa is a small but conspicuous dioicous acrocarpous moss 3–7cm in height with tidy five-ranked squarrose leaves, serrulate distally, and with a luxuriant vestiture of rhizoids up the stems; the sporophytes (not seen) have setae 2.5–4.5 cm and the capsule is 2–3 mm (Vitt 2014a). As described by D. Vitt in the Flora of North America North of Mexico, “Paludella is one of the most spectacular moss species in the flora area” (Vitt 2014a). Paludella is described by H. Crum in Mosses of the Great Lakes Forest, as “one of the most attractive and curious mosses” (Crum 1983) and by Crum and Anderson (1981) as “a most curious moss, of unbelievable appearance. It is very attractive. It resembles no other moss in its densely tomentose stems and extremely squarrose-recurved leaves with the tips folded downward in such a way that they seem heart-shaped.”

Specimen Citations: WISCONSIN: Oconto County: 45.196543, –88.355258 at 290.5m elevation, on a floating peat-sedge mat in a boreal rich fen at the largest inlet to Waupee Lake Swamp at the north end of the lake; September 6, 2021, Wefferling, Berkopec, and Eicchorn 764 (UWGB). 45.196543, –88.355258 at 291m elevation, in peaty soil in a boreal rich fen at the northwest side of Waupee Lake; June 17, 2022, Wefferling and Smith 851 (UWGB). 45.196514, –88.355254 at 291m elevation, in peaty soil in a boreal rich fen at the northwest side of Waupee Lake; June 17, 2022, Wefferling and Smith 861 (UWGB).