Leersia lenticularis Michx.
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Basis for Listing
In Minnesota, Leersia lenticularis (catchfly grass) is limited to forested habitats on the floodplain of the Mississippi River in three southeastern counties, and it is very rare. Most threats to the species and its habitat have already been realized. Early settlers to the region cleared many of the forests for fuel and other purposes, and most of the remaining forests were submerged when a series of dams were built on the river beginning in the 1920s. Threats today are more difficult to assess. River levels are still manipulated to accommodate barge traffic, often with unanticipated effects on native, riverine vegetation. Recent years have also seen an increase in the invasion of non-native species, particularly Phalaris arundinacea (reed canary grass), which renders the species' habitat unsuitable. That was the situation when L. lenticularis was listed as a species of special concern in 1984. Since that time, the Minnesota Biological Survey has completed extensive floristic searches in the southeastern counties and found L. lenticularis to be even rarer than previously thought. Furthermore, threats to its habitat have intensified, as the number of highly invasive, non-native, plant species have increased many times over. For these reasons, the status of Leersia lenticularis was elevated to threatened in 2013.
Leersia lenticularis is a conspicuous, mid-sized, perennial grass. There are three species of Leersia in Minnesota. While all three are superficially similar, L. lenticularis is perhaps the most distinctive. The spikelets of all three species have only a single flower, and the flower lacks glumes and awns. The spikelets are arranged in an open panicle or enclosed in the uppermost leaf sheath. In the case of L. lenticularis, the spikelet is 3-4 mm (0.12-0.16 in.) long (much longer than the other species) and nearly circular in shape (Allison 1959).
All of the habitats of L. lenticularis in Minnesota occur in seasonally flooded forests along the Mississippi River in Wabasha, Winona, and Houston counties (The Blufflands Subsection). These floodplain forests are usually dominated by Populus deltoides (cottonwood) or Acer saccharinum (silver maple). The ground layer is usually sparse, except where there is a depression resulting in a thinner canopy (and more sunlight) or along an edge, especially where the edge adjoins a wetland or riverbank. It is usually along such an edge or under a thin canopy where L. lenticularis occurs.
Biology / Life History
Perhaps the most salient feature of L. lenticularis' biology is its adaptation to annual floods. Floods will scour and erode the soil in many locations and re-deposit it (through the process of siltation) in other locations. Relatively few species are adapted to such harsh conditions.
Conservation / Management
Many of the forces affecting the habitat of L. lenticularis are human-caused but beyond the control of local land managers. For example, the timing and frequency of flooding is largely under the control of the U.S. Army Corp of Engineers, who control the locks and dams on the Mississippi River. Also, water quality is dependent upon upstream pollution and storm water management. Another major concern is the invasion of non-native, plant species particularly Phalaris arundinacea (reed canary grass). No one has yet devised an effective and practical plan for controling this invasive species in natural habitats.
Best Time to Search
The best time to search for L. lenticularis is when reproductive structures are present, from mid-July through September.
Conservation Efforts in Minnesota
When the dams were completed on the Upper Mississippi River, much of the bottomland was flooded, rendering it useless to agriculture and most other economic uses. For this reason (and others), the federal government took ownership of portions of the land and designated it a fish and wildlife refuge. Most of the habitat occupied by L. lenticularis is within this refuge. While this protects the habitat from development, unfortunately, it does not address the bigger concern of water level manipulation on the Mississippi River and the resulting disruption of natural flood cycles.
Welby Smith, MN DNR, 1988, 2008, and 2017
Allison, H. 1959. Key to the grasses of Minnesota found in the wild or commonly cultivated as crops. Department of Botany, University of Minnesota, Minneapolis, Minnesota. 52 pp.
Coffin, B., and L. Pfannmuller, editors. 1988. Minnesota's endangered flora and fauna. University of Minnesota Press, Minneapolis. 473 pp.
Minnesota Department of Natural Resources. 2005. Field guide to the native plant communities of Minnesota: the eastern broadleaf 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. 394 pp.
Minnesota Department of Natural Resources. 2006. Tomorrow's habitat for the wild and rare: An action plan for Minnesota wildlife, comprehensive wildlife conservation strategy. Division of Ecological Services, Minnesota Department of Natural Resources. 297 pp. + appendices.
Minnesota Department of Natural Resources, Division of Ecological Resources. 2008. Rare species guide: an online encyclopedia of Minnesota's rare native plants and animals [Web Application]. Minnesota Department of Natural Resources, St. Paul, Minnesota. Accessed 1 July 2009.
Pyrah, G. L. 1969. Taxonomic and distributional studies in Leersia (Gramineae). Iowa State College Journal of Science 44(2):215-270.
Pyrah, G. L. 2007. Leersia. Pages 42-45 in Flora of North America Editorial Committee, editors. Flora of North America north of Mexico. Volume 24. Oxford University Press, New York, New York.