Synonyms

Schoenus fuscus, Rhynchospora alba var. fusca

  Basis for Listing

Rhynchospora fusca occurs in the Atlantic Coastal Plain region of northeastern North America, and less commonly in the Great Lakes region. The species also occurs in Europe. Rhynchospora fusca was first discovered in Minnesota in 1950 and initially believed to be restricted to water tracks in large, patterned peatland complexes. Although such peatlands likely contain some of the largest populations, the species has since been found in a variety of fen habitats including rich fens, poor fens, and shore fens. Less commonly, it has also been documented from sandy-gravel lakeshores. Populations range from a few individuals to 1,000's of plants.

Nearly 90% of Minnesota's known occurrences of R. fusca are from the Arrowhead region of St. Louis, Lake, and Cook counties. Although difficult to determine what actually constitutes individual populations, it is estimated that around six-dozen populations have now been documented. However, the majority of these populations have not been revisited since their initial discoveries. Rhynchospora fusca was listed as a special concern species in Minnesota in 1984.

  Description

Rhynchospora fusca is a cespitose (growing in tufts) perennial with slender rhizomes. The culms and leaves are filiform; the inflorescence includes several clusters of cinnamon brown to brown spikelets; and the flowers have 5-6 bristles (not to be confused with stamens) that are antrorsely barbed (directed upward). Barbs can sometimes be detected in the field with a good hand lens (10x) and backlight, but are best observed under stronger magnification.

Three species of Rhynchospora are known to occur in Minnesota: R. alba (white beak rush), R. capillacea (hair-like beak rush), and R. fusca. Rhynchospora alba and R. fusca primarily occur in the Laurentian Mixed Forest province of the greater northeastern portion of the state (Minnesota DNR 2003), while R. capillacea, a threatened species, occurs mostly outside this province in the calcareous fens of western and southern Minnesota. An exception to this includes an occurrence of R. capillacea in the Lost River Peatland Scientific and Natural Area in Koochiching County. Rhynchospora fusca is also our only species with antrorsely barbed bristles; the other species are retrorsely barbed (directed downward). Although R. alba typically has whitish spikelets, it can also be brown in color like R. fusca. Determining the direction of the barbs on the bristles will assure positive identification of R. fusca.

  Habitat

Rhynchospora fusca occurs in sunny, wet, acidic, and typically peaty habitats. In Minnesota, these habitats include hummocks of Sphagnum spp. (sphagnum moss) on boggy shores; floating mats at the margins of lakes and bog ponds; boggy pools, puddles and depressions in fens; water tracks of richer or larger peatland complexes; and less commonly on sandy shores. Across its range, R. fusca habitats include sands and peats of pond shores, bogs, and seeps (Kral 2002) and sandy peaty shores, interdunal hollows, sandy excavations, boggy meadows, and occasionally bog mats. It is more often at remnants of bogs and often in somewhat marly places (Voss 1972).

Associated plant species often include R. alba, Scheuchzeria palustris (Scheuchzeria), and Drosera spp. (sundews).

  Biology / Life History

Rhynchospora fusca is a perennial herb that may form tufts or dense mats. It disperses by seed and vegetatively by rhizomes.

The best time to search for R. fusca is between mid-July and mid-August, although plants may be discernable earlier in the season and sometimes into September.

  Conservation / Management

Although we continue to gain a better understanding of the distribution and abundance of rare species, we often know little more. Well-designed monitoring efforts are necessary in order to better understand species ecology and how populations are responding to management activities and a changing environment. The potential threats to R. fusca include outright destruction of habitat and physical, chemical, or hydrological alterations of habitat conditions. Many populations are located in boggy areas where people typically do not recreate. However, these saturated, peaty substrates are readily mucked up and disturbed when visited.

  Conservation Efforts in Minnesota

Many of the known populations of R. fusca occur on state and federal land, and approximately 40% of them occur in areas formally protected and designated as Scientific and Natural Areas or the Boundary Waters Canoe Area Wilderness. Initial botanical surveys have been completed in much of the state and efforts are ongoing in the northernmost subsections of Minnesota including the Border Lakes. It is expected that new populations of R. fusca will be discovered.

  References

Crow, G. E., and C. B. Hellquist. 2000. Aquatic and wetland plants of northeastern North America. Volume 2. Angiosperms: Monocotyledons. University of Wisconsin Press, Madison, Wisconsin. 400 pp.

Kral, R. 2002. Rhynchospora. Pages 200-239 in Flora of North America Editorial Committee, editors. Flora of North America north of Mexico. Volume 23. Oxford University Press, New York, New York.

Minnesota Department of Natural Resources. 2003. Field guide to the native plant communities of Minnesota: the Laurentian mixed forest province. Ecological Land Classification Program, Minnesota County Biological Survey, and Natural Heritage and Nongame Research Program. Minnesota Department of Natural Resources, St. Paul, Minnesota. 352 pp.

Voss, E. G. 1972. Michigan Flora Part I. Gymnosperms and Monocots. Cranbrook Institute of Science Bulletin 55 and the University of Michigan Herbarium. University of Michigan, Ann Arbor, Michigan. 488 pp.