Juncus marginatus Rostk.
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Basis for Listing
All of the available evidence indicates that Juncus marginatus (marginated rush) 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. Although it was listed as special concern in 1996, a status of endangered was considered but thought premature, since there was no certainty it would ever be found in Minnesota again. 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). For this reason, its status was changed to endangered in 2013.
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 5-50 hemispherical flower clusters (called glomerules), each 4-8 mm (0.16-0.31 in.) across. The individual flowers lack subtending bracts. The seeds are tiny, no more than 0.5 mm (0.02 in.) long and lack an appendage (Brooks 2000; Clements 1985).
Juncus marginatus is a species of shallow wetlands and wetland margins (known to ecologists as lowland prairie and wet meadow/carr) 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, though 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 occurred at the time of settlement was a mix of savanna and prairie, 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 in some drought years, indicating that J. marginatus may be fire-adapted.
Conservation / Management
The habitat fragments, where J. marginatus occurs are in a very sensitive to invasion from non-native species fragile condition and need active management to survive. Primarily, it is (future vs present) essential to protect or restore the natural hydrological regime. This might involve removing drain tiles, plugging ditches, re-routing storm water, or relocating wells. It is also important 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 required. The spread of Rhamnus cathartica (common buckthorn) and Phalaris arundinacea (reed canary grass) pose the greatest threat to the species.
Juncus marginatus emerges in May, however, positive identification is easiest when the seed pods are fully developed in August and the first half of September.
Conservation Efforts in Minnesota
The Minnesota DNR has secured the protection of the two largest and best habitats where J. marginatus occurs. One is in a State Scientific and Natural Area, (no SNA mentioned in the EO report) the other is in a State Wildlife Management Area. Management of these sites to maintain habitat conditions conducive to the long-term survival of J. marginatus is hoped for.
Author: Welby Smith, MN DNR, 2008
Revised: Welby Smith, MN DNR, 2016
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. 234 pp.