Page  72 ï~~72 THE MICHIGAN BOTANIST Vol. 48 CALTHA NATANS PALLAS (RANUNCULACEAE) NEW FOR MICHIGAN AND THUNDER BAY DISTRICT, ONTARIO Allan G. Harris Janet Keeney Marr Northern Bioscience 23180 Highway Rd. 136 South Hill St. Calumet, Michigan 49913 Thunder Bay, Ontario P7B 3V1 ABSTRACT We describe newly discovered populations of Caltha natans in Michigan and Thunder Bay District, Ontario. This species is a small aquatic plant distributed in a narrow band from northern Alberta to the Lake Superior area. Its distribution in eastern North America is consistent with dispersal by water along the receding ice front or Lake Agassiz shoreline before 9900 years BP, after which dispersal virtually ceased. Keywords: Caltha natans, Michigan, Ontario, post-glacial dispersal INTRODUCTION Caltha natans Pall. (floating marsh marigold) is a small, irregularly circumpolar aquatic plant with floating or creeping stems that root at nodes. In contrast to its more common relative C. palustris L. (marsh marigold), the heart-shaped, leaf blades of C. natans are smaller (2-5 cm wide) and its flowers (1 cm wide) are white-sepaled (rarely pink) and bloom in June to August (Figure 1). Its North American range includes Alaska, Yukon, Northwest Territories, Nunavut, northern British Columbia and Alberta, extending in a narrow band through Saskatchewan, Manitoba and northwestern Ontario to Minnesota and Wisconsin (Ford 1997) (Figure 2). Habitat for Caltha natans in eastern North America is typically shallow, slow-moving streams often associated with beaver disturbance. Populations occasionally extend into shallow waters of lakes near stream mouths. Plants are usually rooted in shallow water on muddy substrate or stranded on mud flats (pers. obs., Lakela 1965, Lakela 1943, Walton 1994). Lakela (1965) also reported the species in drainage ditches in Minnesota. In Ontario, Caltha natans is ranked as S2 (very restricted range, often 20 or fewer populations) (Natural Heritage Information Centre 2008) and is restricted to the western edge of the province, with the exception of a disjunct record in the Ekwan River Basin approximately 75 km west of James Bay (Figure 2) (Riley 2003). The species is locally common on the Aulneau Peninsula on Lake of the Woods and in the southern part of Woodland Caribou Provincial Park on the Manitoba border (pers. obs. A.G. Harris). Caltha natans is ranked as Endangered in Wisconsin (Wisconsin Department of Natural Resources 2004) and Minnesota (Minnesota Department of Natural Resources 2007). In Wisconsin, it occurs at a single location on the St. Croix River in Douglas County in the northwest corner of the state (Wisconsin State

Page  73 ï~~2009 THE MICHIGAN BOTANIST 73 2009 THE MICHIGAN BOTANIST 73 FIGURE 1. Photo taken September 17, 2007. Malachi Lake area, Kenora District, Ontario (Photo taken by Samuel R. Brinker). Herbarium 2008). In Minnesota, populations have been found at about five locations in St. Louis Co. but some of these populations have apparently disappeared due to habitat destruction (Lakela 1965, Coffin and Pfannmuller 1988). The species was discovered in Voyageurs National Park (St. Louis County) in 1999 (University of Minnesota Herbarium 2009), and near Duluth in the early 1990s (Walton 1994). Subsequent to its discovery in Michigan (described in this paper), Caltha natans was added as Threatened to the Proposed List of Endangered and Threatened Species for Michigan in September 2008 (MDNR 2008). MATERIALS AND METHODS We discovered populations of Caltha natans while conducting fieldwork in Baraga County, Michigan and Thunder Bay District, Ontario. Subsequently we compiled records of this species in eastern North America from published and unpublished sources: ON: White and Riley 1983, Walshe 1980, previously unreported records from A.G. Harris and R.F. Foster 1998 to 2005; MN: Coffin and Pfannmuller 1988, Lakela 1965, Walton 1994, University of Minnesota Herbarium 2009; WI: Wisconsin State Herbarium 2008. RESULTS Baraga County, Michigan On 26 September 2007, Allan Harris (AGH) discovered a population of Caltha natans in a narrow channel draining into Silver River, about 10 km ESE

Page  74 ï~~74 THE MICHIGAN BOTANIST Vol. 48 74 THE MICHIGAN BOTANIST Vol. 48.. r > K " - t - r f i SIL FIGURE 2. North American distribution of Caltha natans (from Ford 1997). Inset area shown in Figure 3. of L'Anse, Baraga County (460 43' N, 880 19' W) (Figure 3). About 12 plants were rooted in about 30 cm of water. (Collection: Marr #3745, MICH). On 16 October 2008, Janet Marr, Pam Nankervis, and Todd Warner observed three additional plants growing nearby in shallow water along the edges of Silver River (associates: Callitriche verna L. and Potamogeton sp.). This population is about 250 km east of the nearest known record, in Wisconsin (Walton 1994). Lac des Mille Lacs, Thunder Bay District Ontario On 25 September 2006 AGH discovered a population of Caltha natans in a small unnamed stream flowing into Gill Lake, east of Lac des Mille Lacs, in Thunder Bay District Ontario (480 58' 26" N, 900 26' 27" W) (Figure 3). About 20 plants were rooted in 20 cm of water at the edges of the stream with Sparganium emersum Rehmann. Substrate was fine sedimentary organic material. (Collection # AGH-06-122, LKHD). The species was not previously known in Thunder Bay District (Thunder Bay Field Naturalists 2003). The Lac des Mille Lacs population is about 130 km northeast of the nearest known record, in Quetico Provincial Park (Walshe 1980).

Page  75 ï~~2009 THE MICHIGAN BOTANIST 75 2009 THE MICHIGAN BOTANIST 75 ee "eee "oee"ess MB 'UQW srr rr " sr"""r" i " " " r" " " " " " " " " " " " James Bay ON Lake of the Wood MN " *........ Lac des *Â~VMille Lacs w........ Ice Margin 9900 BP Caltha natans Records * Previous Records S New Records S @0 0 50 0 50 100 Kilometers IWE~m/l FIGURE 3. Distribution of Caltha natans in eastern North America relative to the position of the Laurentian Ice Sheet c 9990 years BP (Teller et al. 1983). All known records from Ontario, Minnesota, Wisconsin, and Michigan are shown. DISCUSSION Caltha natans is relatively widely dispersed within about 100 km south of the position of the Laurentide Ice Sheet at about 9900 years BP (Figure 3) (Teller et al. 1983). The species apparently did not disperse to the northeast as the ice retreated, despite abundant potential habitat through northern Ontario. In contrast, some genera of aquatic plants (Potamogeton, Myriophyllum, Isoetes) apparently closely followed the receding ice sheet (Dieffenbacher-Krall and Jacobson 2001). Caltha fruits are unspecialized for long-distance transportation by wind or animals (Schuettpelz and Hoot 2004) and water appears to be the most likely dispersal mechanism. The distribution of Caltha natans in central North America is consistent with dispersal by water along the receding ice front or Lake Agassiz shoreline before 9900 years BP, after which dispersal virtually ceased. The outlier near James Bay, however, does represent a more recent dispersal since this area was covered by ice or seawater until about 7200 years BP (Thorleifson 1996). Although apparently quite rare in eastern North America, additional populations of Caltha natans may yet be discovered in northwestern Ontario, Min

Page  76 ï~~76 THE MICHIGAN BOTANIST Vol. 48 nesota, northern Wisconsin, and the Upper Peninsula of Michigan within about 100 km of the 9900 years BP ice margin. ACKNOWLEDGMENTS Edward Voss and Tony Reznicek (University of Michigan Herbarium) verified the identification of Caltha natans and helped in getting this species added to the proposed list of endangered and threatened species in Michigan. The Keweenaw Bay Indian Community (KBIC) with a grant from the U.S. Fish and Wildlife Service funded the study that resulted in the discovery of C. natans in Michigan. Pam Nankervis and Todd Warner (KBIC) assisted in locating additional C. natans plants. Matt Boyd at Lakehead University provided information on Lake Agassiz. Rob Foster, Mike Oldham, Tony Reznicek, Wasyl Bakowsky, and Edward Voss commented on an earlier draft of this paper. Sam Brinker provided the photograph. LITERATURE CITED Coffin, B. and L. Pfanmuller, editors. (1988). Minnesota's Endangered Flora and Fauna. University of Minnesota Press, Minneapolis. Dieffenbacher-Krall, A. C. and G. L. Jacobson Jr. (2001). Post-glacial changes in the geographic ranges of certain aquatic vascular plants in North America. Biology and Environment: Proceedings of the Royal Irish Academy. 101B (1-2): 79-84. Ford, B. A. (1997). Caltha. In N. R. Morin [ed.], Flora of North America north of Mexico, vol. 3. Oxford University Press. Oxford. Lakela, O. (1943). The rediscovery of Caltha natans in Minnesota. Rhodora 45:53-55. Lakela, O. (1965). A Flora of Northeastern Minnesota. University of Minnesota Press, Minneapolis. Michigan Department of Natural Resources (MDNR). (2008). Proposed list of endangered and threatened species, Wildlife Division, Lansing, Michigan. specialplants.cfm Accessed January 2009 Minnesota Department of Natural Resources (DNR). (2007). Minnesota's List of Endangered, Threatened, and Special Concern Species. endlist.pdf Accessed 15 January 2009. Natural Heritage Information Centre (NHIC). (2008). Natural Heritage Information Centre website. Ontario Ministry of Natural Resources. Accessed December 2008. Riley, J. L. (2003). Flora of the Hudson Bay Lowland and its Postglacial Origins. NRC Research Press. Ottawa. Schuettpelz, E. and S. B. Hoot. (2004). Phylogeny and biogeography of Caltha (Ranunculaceae) based on chloroplast and nuclear DNA sequences. American Journal of Botany. 91:247-253. Teller, J. T., L. H. Thorleifson, L. A. Dredge, H. C. Hobbs, and B. C. Schreiner. (1983). Maximum extent and major features of Lake Agassiz. In J. T. Teller, and L. Clayton. eds. Glacial Lake Agassiz. Geological Association of Canada Special Paper 26. Thorleifson, L. H. (1996). Review of Lake Agassiz history. In: Teller, J. T., L. H. Thorleifson, G. Matile, and W. C. Brisba. eds. Sedimentology, Geomorphology, and History of the Central Lake Agassiz Basin. Geological Association of Canada Fieldtrip Guidebook B2, 55-84. Thunder Bay Field Naturalists (TBFN). (2003). Checklist of the Vascular Plants of Thunder Bay District. Lakehead University. University of Minnesota Herbarium. (2009). J. F. Bell Museum of Natural History Herbarium Vascular plant collection database. Accessed January 2009. Walshe, S. (1980). Plants of Quetico and the Ontario Shield. University of Toronto Press. Toronto. Walton, G. B. (1994). Report for Field Season 1994. Status survey for Caltha natans and Sparganium glomeratum in Minnesota. Conservation Biology Research Grants Program Natural Heritage and Nongame Research Program. Division of Ecological Services. Minnesota Department of Natural Resources. online at: 1994_walton.pdf White, D. J. and J. L. Riley. (1983). Caltha natans Pallas. In K. M. Pryer and G. W. Argus. eds. Atlas

Page  77 ï~~2009 THE MICHIGAN BOTANIST 77 of the rare vascular plants of Ontario. Part 4. National Museum of Natural Sciences, Ottawa. (looseleaf). Wisconsin Department of Natural Resources (DNR). (2004). Wisconsin Endangered and Threatened Species Laws & List. Accessed 15 January 2009. Wisconsin State Herbarium. (2008). Wisconsin State Herbarium Website Accessed December 2008.