Rare Species Guide

  Synonyms

Muhlenbergia uniflora var. terrae-novae, Sporobolus uniflorus

  Basis for Listing

Muhlenbergia uniflora is a small, fine grass primarily distributed in northeastern North America and ranging as far west as Minnesota. Several outlier populations occur in British Columbia, Oregon, and possibly Texas, where the populations have likely been introductions (Peterson 2003). The species was first reported in Minnesota from St. Louis County in 1956 and from Lake County the following year. The St. Louis County occurrence near Gilbert has never been relocated. It is also questionable whether the Lake County location has been relocated, in part due to disputed herbarium label data. Muhlenbergia uniflora subsequently went undocumented in the state until 1987, when it was discovered on the sandy beaches of a lake in the Boundary Waters Canoe Area Wilderness. As of 2009, approximately 25 occurrences had been reported; many of which are within 7 km (4.5 mi.) of each other.

All recent locations of this species are within the Border Lakes and Laurentian Uplands ecological subsections (Minnesota DNR 2009). Although what appears to be suitable habitat may be scattered across portions of the Arrowhead region, M. uniflora remains poorly documented. Whether this is due solely to rarity or in part due to its inconspicuous nature is yet to be determined. Monitoring studies have never been conducted on Minnesota populations. Muhlenbergia uniflora was listed as a special concern species in Minnesota in 1996.

  Description

Muhlenbergia uniflora is a very fine and wispy plant growing in small, loose tufts or mats. Culms are 5-45 cm (2.0-17.7 in.) long, sometimes becoming decumbent and rooting at the base. The inflorescence is an open panicle. The tiny, purple spikelets (< 2 mm; 0.08 in.) are 1(-2) flowered, often on long pedicels and subtended by glumes shorter than the lemmas.

  Habitat

In Minnesota, M. uniflora occurs in wetlands and is considered to be a wetland obligate species (Milburn et al. 2007). It occurs along sandy-gravel shores or cobbly organic shores, in seasonal basins, in peaty depressions, and on low hummocks in rich sedge fens. Habitats are also often seasonally or intermittently inundated resulting from snow melt, rains, or beaver influences. Muhlenbergia uniflora may appear in a band or zone near the upper reaches of exposed shorelines or scattered throughout the exposed bottoms of shallow basins. It has also been collected from weakly acidic fens, beaver influenced meadows, and from natural drainages and trail edges typically having thin, peat-mats over sand-gravel-cobble or bedrock substrates.

Across its range, M. uniflora is also known to occur in bogs, wet meadows, and lake shores in sandy or peaty, often acidic, soils; damp, sandy lakeshores, often becoming abundant following lowering of water levels; meadows and swamp borders; and margins of rock pools at Isle Royale (Voss 1972; Peterson 2003).

Muhlenbergia uniflora is very fine and wispy and nearly undetectable when growing amongst other fine graminoids, which it often does. Associated plant species may include Agrostis scabra (rough bentgrass), Dichanthelium acuminatum (hairy panic grass), Carex cryptolepis (secretive sedge), Rhynchospora spp. (beak rushes), Chamaedaphne calyculata (leatherleaf), Myrica gale (sweet gale), and Persicaria amphibia (water smartweed).

  Biology / Life History

Muhlenbergia uniflora is a non-rhizomatous, perennial grass that disperses via seed. It may occur in small, local patches of plants or large robust populations of 1,000s of culms. It develops buds from below the nodes, which on decumbent culms produce new flowering culms (Voss 1972). Although it can be found growing in a variety of wetland habitats, M. uniflora is often associated with wetlands or ecotones that undergo seasonal lowering of water levels, which further expose suitable habitat. In some instances, water levels and fluctuations are influenced by pooling or draining associated with the presence and maintenance (or lack thereof) of beaver dams. Beaver activity is a dynamic component of the northern forest ecosystem and the specifics of how such activities influence the short or long-term survival of M. uniflora is not understood and likely pondered by few.

The best time to search for M. uniflora is when the plant is fully developed in later flower or fruit, usually from mid-August to early September. Prime times may fluctuate depending upon availability of exposed habitats.

  Conservation / Management

Other than becoming a little more successful in determining where this species may occur, populations are not being further monitored. Well-designed monitoring efforts are necessary in order to better understand species ecology and how populations are responding to management activities, natural disturbance events, and a changing environment. Potential threats to M. uniflora include outright destruction of habitat and physical, chemical, or hydrological alteration of habitat conditions. Opportunities currently exist across several land ownerships to learn more about the biology and ecology of this rare wetland species.

  Conservation Efforts in Minnesota

All but one of the known occurrences of M. uniflora are within the jurisdictional boundaries of the Superior National Forest. Most occur on federal lands, several are upon state land, and over half are within the Boundary Waters Canoe Area Wilderness. The DNR's Minnesota Biological Survey is currently surveying in portions of the Border Lakes subsection of northeastern Minnesota, and it is likely that new populations will be recorded.

  References and Additional Information

Milburn, S. A., M. Bourdaghs, and J. J. Husveth. 2007. Floristic quality assessment for Minnesota wetlands. Minnesota Pollution Control Agency, St. Paul, Minnesota. 197 pp.

Minnesota Department of Natural Resources. 2003. Field guide to the native plant communities of Minnesota: the Laurentian mixed 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. 352 pp.

Minnesota Department of Natural Resources. 2009. Ecological Classification System. . Accessed 13 April 2009.

Peterson, P. M. 2003. Muhlenbergia. Pages 145-200 in Flora of North America Editorial Committee, editors. Flora of North America north of Mexico. Volume 25. Oxford University Press, New York, New York.

Voss, E. G. 1972. Michigan Flora: Part I Gymnosperms and Monocots. Cranbrook Institute of Science Book 55, Bloomfield Hills, Michigan. 488 pp.