Juncus marginatus Rostk.
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Basis for Listing
All of the available evidence indicates that Juncus marginatus has always been very rare in Minnesota. In fact, for the better part of a century it was thought to occur at only one site, a small sand dune/wetland complex in Fridley (Anoka County). When that site was destroyed in 1960, it was feared that J. marginatus was gone from the state. However, efforts to rediscover the species yielded unexpected results in 1999 when a cluster of small colonies was found in isolated habitat fragments near Blaine (Anoka County). Juncus marginatus was listed as a special concern species in Minnesota in 1996, however, elevating its status to endangered is currently being considered.
Compared to other rushes, J. marginatus is relatively small and slender, almost grass-like in appearance. The stems can reach 50 cm (20 in.) tall. The leaves are flat, not septate, and only 1-3 mm (0.04-0.12 in.) wide. The inflorescence has 5-20 heads, each 4-6 mm (0.16-0.24 in.) across. The individual flowers lack subtending bracts. The seeds are tiny, less than 1 mm (0.04 in.) long and lack an appendage.
Juncus marginatus is a species of shallow wetlands and wetland margins on the Anoka Sandplain. These habitats develop where depressions in the land dip slightly below the water table allowing water to saturate the otherwise well-drained, sandy soil. Low-stature sedges and rushes usually dominate these habitats although scattered shrubs or clumps of shrubs, particularly Salix spp. (willows), Cornus spp. (dogwoods), and Rubus spp. (bristle-berries and dew-berries), will also be present.
Biology / Life History
Juncus marginatus is a short-lived perennial that occurs in low densities among other rushes, sedges, and grasses. Apparently it never becomes abundant enough to dominate a habitat, at least not in the Minnesota habitats where it has been studied. The flowers are wind-pollinated and the seeds are either gravity-dispersed or insect-dispersed. The general landscape where J. marginatus occurs was a mix of savanna and prairie at the time of settlement, so wildfire would have been a common occurrence. It is unclear how often those fires would have burned the intervening wetlands where J. marginatus occurs, but it probably did happen during some drought years, indicating that J. marginatus may be fire-adapted.
Conservation / Management
The habitat fragments where J. marginatus occurs are in a very fragile condition and need active management to survive. Primarily, it will be necessary to protect or restore the natural hydrological regime. This might involve removing drain tiles, plugging ditches, re-routing storm water, or relocating wells. It will also be necessary to protect the sites from non-compatible recreational uses, especially off-road motorized vehicles. And because the habitat fragments have been isolated from the ecosystem processes that would normally maintain them, vegetation management to control encroaching shrubs and invasive species is needed. The spread of Rhamnus cathartica (common buckthorn) and Phalaris arundinacea (reed canary grass) pose the greatest threat to the species.
Conservation Efforts in Minnesota
There are efforts being made by the Minnesota DNR to secure the protection of the largest and best habitat where J. marginatus occurs. At this time, it is unclear what the results of these efforts will be.
Brooks, R. E. 2000. Juncus subgenus graminifolii. Pages 225-233 in Flora of North America Editorial Committee, editors. Flora of North America north of Mexico. Volume 22. Oxford University Press, New York, New York.
Clements, S. E. 1985. A key to the Rushes (Juncus spp.) of Minnesota. The Michigan Botanist 24:33-37.
Wovcha, D. S., B. C. Delaney, and G. E. Nordquist. 1995. Minnesota's St. Croix River Valley and Anoka Sandplain, a guide to native habitats. University of Minnesota Press, Minneapolis, Minnesota. 234 pp.