Diarrhena obovata (Gleason) Brandenburg
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Diarrhena americana var. obovata
Basis for Listing
Diarrhena obovata (obovate beakgrain) was not known to occur in Minnesota until a moderately large population was discovered along the Root River in Fillmore County in 1994 (Blufflands Subsection). It seems fairly certain that this population is not a recent introduction. It is presumably an outlier population, occurring at the edge of its natural range. It was immediately recognized as very rare in Minnesota, however, little else was known about it. Because of these uncertainties, it was designated a species of special concern in 1996. A more protective status was considered at the time but was deferred until a more thorough search could be made of potential habitat. Ultimately, those searches were conducted by the Minnesota Biological Survey, and yet no additional populations of D. obovata were found. For this reason, its status was elevated to endangered in 2013.
Diarrhena obovata is listed as endangered in Wisconsin and threatened in Michigan. It is apparently secure in Iowa, especially in the southern half of the state.
Diarrhena obovata is a rather large, woodland grass that forms loose patches on the forest floor. The stems can grow to about 1.0 m (3.3 ft.) tall. The leaves are nearly as long and up to 1.8 cm (0.7 in.) wide. The inflorescence is 10-30 cm (3.9-11.8 in.) long and it droops or arches. Each spikelet has 3-5 flowers and is 10-16 mm (0.4-0.6 in.) long. The first glume has 1 nerve, and the second glume has 3-5 nerves (Brandenburg 2007).
There is only one known population of D. obovata in Minnesota. It occurs in a mature mesic hardwood forest along the Root River on both the broad, alluvial terrace (Southern Terrace Forest) and the north-facing slope of the bluffs above the terrace (Southern Mesic Oak-Basswood Forest). The dominant canopy trees are Acer saccharum (sugar maple), Tilia americana (basswood), Celtis occidentalis (hackberry), Quercus rubra (northern red oak), Q. macrocarpa (bur oak), and Q. alba (white oak). The soils have been described as silt and silty-loam. In other states, the species is apparently more closely associated with active floodplains, where the soils would likely be silt.
Biology / Life History
Nothing specific is known about the biology or life history of D. obovata, except what can be inferred from its morphology and habitat. For example, it can reproduce from an underground rhizome, indicating that reproduction by seed may not be important in the short term. Evidently, it is also tolerant of continuous shade, full sunlight, and seasonal flooding of short duration.
Conservation / Management
Forest clearing, livestock grazing, and the invasion of aggressive, non-native species, especially Rhamnus cathartica (common buckthorn) and Alliaria petiolaris (garlic mustard) pose the greatest threat to D. obovata and its habitat. A primitive campsite, accessible by a two-track forest road, is present in the immediate vicinity of the only known Minnesota population. Any upgrading of the forest road or forest clearing that would accompany campsite improvements or conversion to permanent housing could significantly impact the population. The best conservation strategy for D. obovata is to maintain the forest canopy and leave the ground layer undisturbed.
Best Time to Search
The best time to search for D. obovata is when mature reproductive structures are present, from early July through mid-September.
Welby Smith, MN DNR, 2008; Welby Smith and Michael Lee, MN DNR, 2017
Brandenburg, D. M. 2007. Diarrhena. Pages 64-66 in Flora of North America Editorial Committee, editors. Flora of North America north of Mexico. Volume 24. Oxford University Press, New York, New York.
Brandenburg, D. M., J. R. Estes, and S. L. Collins. 1991. A revision of Diarrhena (Poaceae) in the United States. Bulletin of the Torrey Botanical Club 118:128-136.
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, 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.
Minnesota Department of Natural Resources, Division of Fish and Wildlife. 1995. Statement of need and reasonableness in the matter of proposed amendment of Minnesota Rules, Chapter 6134: endangered and threatened species. Minnesota Department of Natural Resources, St. Paul, Minnesota. 336 pp.
O'Connor, R. P., and M. R. Penskar. 2004. Special plant abstract for Diarrhena americana (American Beak