Fimbristylis puberula var. interior (Britt.) Kral
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Basis for Listing
Minnesota populations of Fimbristylis puberula var. interior are entirely restricted to calcareous fens. These small groundwater-fed wetlands are rich in calcium and magnesium bicarbonates and low in dissolved oxygen. They are also very fragile, and extremely vulnerable to changes in groundwater levels. There are over 100 calcareous fens known to occur in Minnesota, but only two fens, one in Redwood County and one in Wilkin County, are known to harbor this rare species. For this reason, F. puberula var. interior was listed as an endangered species in 1996.
Fimbristylis puberula var. interior is a perennial member of the sedge family that grows from short stout knotty rhizomes. Rhizomes of variety interior are more slender and numerous then variety puberula. Stems are slender and smooth and are either solitary or in small tufts. Leaves are smooth or occasionally hairy, usually only 1 mm (0.04 in.) wide and strongly involute (rolled-up lengthwise). The ligule is present in this variety although absent from variety puberula. The longest involucre bract usually surpasses the flowers (unlike var. puberula where the bract is shorter than the flowers), and the spikelets are 5-10 mm (0.2-0.4 in.) long (Gleason and Cronquist 1991).
The two populations known to occur in Minnesota are in calcareous fens. Fens are saturated, peat-filled wetlands sustained by upwelling groundwater. They are open (non-forested) habitats dominated by Carex spp. (sedges) and Juncus spp. (rushes). Associated species of F. puberula var. interior include other rare species such as Scleria verticillata (whorled nut-rush) and Rhynchospora capillacea (hair-like beak-rush), and the more common Lobelia kalmii (Kalm's lobelia) and Triglochin palustris (marsh arrowgrass).
Biology / Life History
Fimbristylis puberula var. interior is a perennial species that flowers from July to October. Flowers are wind-pollinated. The mechanism for seed dispersal is not known.
Conservation / Management
Both of the calcareous fens where F. puberula var. interior were found are on private land and have experienced some level of degradation because of incompatible land use practices. Of paramount importance is the maintenance of the natural hydrological regime that sustains the fens. It is also important to exclude livestock and prevent surface erosion and sedimentation. Periodic dormant season fire may be helpful in controlling encroaching shrubs, but must be timed carefully to avoid damaging the plants.
Conservation Efforts in Minnesota
Although the Wetland Conservation Act of 1991 currently provides special protection for calcareous fens, the very limited number of occupied sites makes F. puberula var. interior vulnerable to extirpation from random or catastrophic events. The DNR's Minnesota Biological Survey has recently searched for rare biological features in the two counties where this species is known to occur. Because additional populations have not yet been discovered, the ecological significance of these two sites is elevated and they warrant special protection.