Fimbristylis autumnalis (L.) Roemer & J.A. Schultes
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Basis for Listing
Fimbristylis autumnalis is a common plant in parts of the eastern United States, especially on the Atlantic coastal plain. It is, however, rare or uncommon in Minnesota and surrounding states. It also seems to have very stringent habitat requirements that are not often encountered in Minnesota. The greatest concentration of plants is in wet meadows and along the margins of shallow lakes or ponds on the Anoka Sand Plain. These habitats are strongly influenced by seasonal ground water fluctuations and the local hydrological setting. In nearly all cases these are fragile habitats, vulnerable to a variety of human-induced changes on the landscape.
There are 16 species of Fimbristylis in the United States, but only two occur in Minnesota: F. autumnalis and F. puberula var. interior (hairy fimbry). The two are somewhat similar but not difficult to tell apart. Fimbristylis autumnalis is a small, annual sedge with smooth, tufted stems 5-20 cm (2.0-7.9 in.) tall. The leaves are basal and usually shorter than the stem, narrowly linear (grasslike), flat, 1-3 mm (0.04-0.12 in) wide, and have scabrid-ciliate margins. The inflorescence is terminal, compound, mostly diffuse, and about as broad as long. The flowers are in narrow red-brown or brown spikelets 3-7 mm (0.12-0.28 in.) long. The seeds (achenes) are pale brown, 3-sided in cross section, obovoid in shape, and 0.5-0.7 mm (0.020-0.028 in.) long (Kral 2002). In contrast to F. autumnalis, F. puberula var. interior is a perennial species that grows much larger. Its stems may reach 50 cm (20 in.) in length and both the spikelets and the achenes are measurably larger.
The sedge meadows where F. autumnalis occurs are typically on nearly level terrain where the water table is at or very near the surface. Slight depressions in the terrain may have ponded water for much of the season and support tall, lush growth of Typha spp. (cattails) and Schoenoplectus spp. (bulrushes). Typically, F. autumnalis occurs at slightly higher elevations where the soil surface is only moist and the vegetation is dominated by short-stature Carex spp. (sedges). The substrate is usually sandy with perhaps a thin layer of organic material such as peat. Fimbristylis autumnalis also occurs on sandy or gravelly lake shores. Such habitats are likely under water in the spring, becoming gradually exposed as the water recedes during the summer. This exposed shoreline is often called the "drawdown" zone and is nearly devoid of vegetation except for a small number of specialized plants.
Biology / Life History
Fimbristylis autumnalis is an annual, meaning it dies at the end of each growing season leaving only seeds to perpetuate the population. Reportedly, the seeds remain dormant when they are submerged in water but can germinate any time during the growing season if their habitat becomes exposed (Baskin et al. 1993). In wet years or years when there is above average summer rainfall, habitats may be underwater all season, and perhaps no F. autumnalis will appear. This is part of the normal range of habitat variability and should not be a problem for F. autumnalis. Presumably the population of seeds can remain dormant for a year or more and germinate whenever conditions are more favorable.
Conservation / Management
Practical guidelines for the management of a habitat where F. autumnalis has been found are difficult to prepare in advance. Each case will need to be addressed individually, although there are some guiding principles that might prove useful. Maintaining the natural hydrologic patterns and the native vegetation are perhaps the most important; the loss of the first invariably leads to the loss of the second. Once these features are lost, it is nearly impossible to restore or recreate them artificially. In fact, attempts to mitigate the loss of high-quality wetlands on the Anoka Sand Plain by creating artificial wetlands elsewhere has a history of failure.
Conservation Efforts in Minnesota
Three populations of F. autumnalis are in habitats owned and managed by local units of government. The management goals at each site emphasize maintenance of the natural features, including rare plant species. One additional site in private ownership is currently protected by an easement and efforts to designate the site as a Scientific and Natural Area are in progress. These four sites only represent approximately 12% of the known populations, so efforts to protect the other populations are critical to the survival of the species in Minnesota.