Rare Species Guide

  Basis for Listing

Poa paludigena (bog bluegrass) is a small inconspicuous grass species that appears to be rare or endangered in every jurisdiction across its range. Its range is notably small and consists of relatively few states in northeastern United States. At one time it was considered for listing as a federally threatened species. It was not known to occur in Minnesota until 1980, when it was discovered during the botanical inventory of the Kettle River Scientific and Natural Area in Pine County (Mille Lacs Uplands Subsection). Subsequent searches have located additional sites in several east-central counties (Laurentian Mixed Forest Province) and one southeastern county (The Blufflands Subsection).  All populations appear to be quite small and are localized in restricted vulnerable wetland habitats. Poa paludigena was listed as an endangered species in Minnesota in 1984 but was reclassified as threatened in 1996.

  Description

Specimens of P. paludigena can show considerable variation and may be very difficult to identify. In particular, the species bears a close resemblance to P. sylvestris (woodland bluegrass) and P. alsodes (wood bluegrass) but can be distinguished from these species by the following combination of characters: lemmas have 3 distinct, pubescent nerves and 2 obscure, intermediate, glabrous nerves. The stem is usually single with only 2 or 3 leaves, each 1-2 mm (0.04-0.08 in.) wide. Lower panicle branches are typically in fascicles of 2.

  Habitat

In Minnesota, populations of P. paludigena occur only in forested wetland habitats that are maintained by groundwater seeps. These may include swamps, margins of small pools, or rivulets of water. Such areas are often dominated by Fraxinus nigra (black ash), Betula alleghaniensis (yellow birch), and sometimes Alnus incana ssp. rugosa (speckled alder). Habitats often develop at the base of a slope or sandstone escarpment where the groundwater seeps out, sometimes on moss or sphagnum hummocks. Associated species include Symplocarpus foetidus (skunk cabbage), Caltha palustris (common marsh marigold), and several sedge species, especially Carex bromoides (brome-like sedge).

  Biology / Life History

Poa paludigena is a short-lived, possibly annual grass species that relies exclusively on seeds for reproduction. The flowers are assumed to be wind-pollinated, and the seeds are thought to be passively dispersed. It has a very small root system that requires a moist or wet environment and appears to rely on a mycorrhizal association with soil fungi. Populations are typically very small and may consist of relatively few individuals confined to small segments of habitat. Some unknown mechanism allows such small isolated populations to remain viable over long periods of time.

  Conservation / Management

Potential threats center on the delicate nature of the species' wetland habitat. Drainage modifications could alter water levels with harmful results. Poa paludigena is not an emergent species. It is perched upon a wet substrate, such as moss, rotting logs, and sedge hummocks. An increase in water level could inundate the plants; a decrease in water level could dry out the substrate and result in desiccation of the plants (Bender 1986). These changes can result from alterations in land or water use in recharge areas that may be quite distant from the seeps themselves. The effects of agricultural run-off have not been analyzed but could alter water chemistry and temperature and could carry sediment, pesticides, or other contaminants. Habitat destruction through drainage for agriculture or canopy removal from forest management are also potential threats (NatureServe 2021).

  Best Time to Search

The best time to search for Poa paludigena is when the florets are fully developed, usually from mid-May to late June.

  Conservation Efforts in Minnesota

There are populations of P. paludigena on public lands that are managed for conservation purposes; however, off-site threats are still a concern.

  Authors/Revisions

Welby R. Smith (MNDNR), 2023

(Note: all content ©MNDNR)

  References and Additional Information

Bender, J. 1986. Element Stewardship Abstracts for Poa paludigena and Napaea dioica. The Nature Conservancy, Midwest Regional Office, Minneapolis, Minnesota.

NatureServe. 2021. NatureServe Explorer [web application]. NatureServe, Arlington, Virginia. (https://explorer.natureserve.org/). Accessed 21 June 2021.

Nekola, J. C. 1990. Rare Iowa plant notes from the R. V. Drexler Herbarium. Journal of the Iowa Academy of Science 97(2):55-73.

Ownbey, G. B., and T. Morley. 1991. Vascular plants of Minnesota: a checklist and atlas. University of Minnesota Press, Minneapolis. 320 pp.

Ownbey, G. B., and W. R. Smith. 1988. New and noteworthy plant records for Minnesota. Rhodora 90:369-377.

Smith, W. 1989. Status Report on Poa paludigena (Bog bluegrass) in Minnesota. Biological Report No. 3. Minnesota Department of Natural Resources, St. Paul. 9 pp.

Soreg, R. J. 2007. Poa. Pages 486-601 in Flora of North America Editorial Committee, editors. Flora of North America north of Mexico. Volume 24. Oxford University Press, New York, New York.

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. 248 pp.