Agrostis hyemalis (Walt.) B.S.P.
Agrostis hyemalis var. hyemalis
Basis for Listing
Our knowledge of Agrostis hyemalis (winter bentgrass) in Minnesota involves a 94-year mystery. It started on June 4, 1902, when a herbarium specimen of this species was collected at an unknown location in Winona County. No one saw the species again until June 21, 1996, when a botanist with the Minnesota Biological Survey found it in Fillmore County. It was discovered while inventorying the plants growing in a small natural area near the town of Rushford (therefore, both specimens were collected on the Paleozoic Plateau). At the time of this writing, the Rushford population is the only one known in Minnesota. While it is possible that other populations do exist, extensive searches have failed to find any. This leads us to the conclusion that A. hyemalis is a very rare species in Minnesota, hence its listing as an endangered species in 2013.
Although Agrostis hyemalis is quite rare in Minnesota, it is relatively common in states to the south and east (Harvey 2007). It is a well-known phenomenon that plant species with the center of their distribution in the southeastern United States often start to diminish in abundance as they approach the significantly drier and colder climate of Minnesota. It is speculated that the hardy individuals that do survive here have unique genetic material and warrant protection for that reason.
The habitat of A. hyemalis is also quite rare in Minnesota. This is the result of the limited extent of sand terrace habitat in the valleys of the Blufflands and the destruction of habitat by over-grazing, sand mining, forest succession, pine-plantations, and development. Increasing development is of special relevance to the habitat in Rushford, because new homes and a new high school have been recently built nearby.
Agrostis hyemalis is a smallish, wispy-looking grass that can easily escape detection. When a candidate has been found, special care must be taken with its identification, since it is often confused with A. scabra (rough bentgrass), a common species that occurs throughout Minnesota (Harvey 2007).
Within the flower, the lemma of A. hyemalis is shorter than the lemma of A. scabra (0.8 - 1.2 mm vs. 1.4 - 2mm [0.03-0.04 in. vs. 0.06-0.08 in.]), and the anthers are very short (about. 0.3 mm vs. 0.4–0.8 mm [0.01 in.vs. 0.02-0.03 in.]). The inflorescence of A. hyemalis differs from that of A. scabra in having the spikelets crowded in spike-like clusters at the ends of the panicle branches, on pedicels up to 1.5–2 mm (0.06-0.08 in.) long. In A. scabra, the spikelets are not so crowded, with at least some of the pedicels exceeding 2 mm (0.08 in) in length. Also, A. hyemalis flowers much earlier in the year than does A. scabra (June vs. July) (Reznicek et al. 2011).
The habitat at the only known site of A. hyemalis in Minnesota is a sand prairie/black oak savanna. The plants grow in full sunlight and partial shade. This is probably similar to the native habitats where this species is found more commonly to the south and east of Minnesota. Yet published reports make it clear that at the heart of its range, A. hyemalis is not restricted to native habitats. It also occurs where human alterations of the landscape have created dry, open and sandy habitats, where this species’ ecological requirements can be met (Reznicek et al. 2011; Harvey 2007).
Biology / Life History
Agrostis hyemalis can function as both an annual and a perennial, depending on growing conditions. It germinates quickly in the spring and may reach maturity and release seeds before the end of June. This accelerated life cycle may be an adaptation to the dry and harsh environment in which it lives. Species with this type of life cycle, and which occur in this type of habitat, often depend on a bank of viable seeds in the soil to maintain population stability. It is not known if this is the case with A. hyemalis.
In late summer, when the inflorescence of A. hyemalis has matured, it breaks off from the stem and blows about in the wind, potentially dispersing its seeds great distances like the classic tumble weed of the open plains (Harvey 2007).
Agrostis hyemalis appears to be a poor competitor, in the sense that it occurs where the vegetation is sparse and of low stature. For example, competition for sunlight from a canopy of trees or competition for moisture from a dense sod of rhizomatous grasses would likely preclude the establishment of A. hyemalis. Furthermore, the dry and exposed nature of its habitat indicates that populations of A. hyemalis are at least occasionally exposed to wildfire.
Conservation / Management
Conservation of the only known site of this species in Minnesota must be considered a priority. While specific management needs for A. hyemalis are unknown, it is reasonable to assume that any management practice that can maintain the diverse native plant community in which it occurs will benefit A. hyemalis as well. The prairie/savanna community where this species is found is normally maintained by wildfire. Since wildfires rarely occur these days, prescribed burns, conducted on a rotation of approximately 5 years, may serve the same function. Although the response of A. hyemalis to fire is unknown, the above-ground life cycle of this species begins in May and is completed in June; therefore, burns should be conducted either before or after this period, not during.
In habitats such as this, soil disturbance caused by vehicles almost always results in an increase of non-native species such as Centaurea stoebe (spotted knapweed) and Berteroa incana (hoary alyssum). Invasion of aggressive non-native plants must be monitored closely. Corrective action, if necessary, needs to be taken quickly.
All of the preceding management activities would benefit not only A. hyemalis, but also a suite of other rare sand prairie species that are known to occur at this site including Phemeranthus rugospermus (rough-seeded fameflower), Asclepias amplexicaulis (clasping milkweed), Baptisia bracteata var. glabrescens (plains wild indigo), Tephrosia virginiana (goat’s rue), and Crocanthemum candense (Canada frostweed).
Best Time to Search
Positive identification of A. hyemalis requires that the specimen have a fully developed inflorescence. Although there is little information on when this occurs in the one Minnesota population, a best estimate is June.
Welby R. Smith (MNDNR), 2018
(Note: all content ©MNDNR)
References and Additional Information
Harvey, M. J. 2007. Agrostis. Pages 633-662 in Flora of North America Editorial Committee, editors. Flora of North America north of Mexico. Volume 24. Oxford University Press, New York.
Marinelli, J., and J. M. Randall, editors. 1996. Invasive plants: weeds of the global garden. Brooklyn Botanic Garden, Brooklyn, New York. 111 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.
NatureServe. 2009. NatureServe Explorer: an online encyclopedia of life [web application]. Version 7.1. <http://www.natureserve.org/explorer>. Accessed 26 June 2009.
Reznicek, A. A., E. G. Voss, and B. S. Walters. 2011. Michigan Flora Online. University of Michigan. <http://www.michiganflora.net/species.aspx?id=1995>. Accessed 22 January 2013.