Shinnersoseris rostrata (Gray) S. Tomb
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Basis for Listing
This distinctive annual is largely restricted to sand dunes in the Great Plains, and it is local or uncommon over most of its range. In Minnesota, Shinnersoseris rostrata is extremely rare. Prior to 1986, the sole known occurrence was in Norman County. In 1986 it was discovered at three additional locations in adjacent Polk County, but all of the locations are part of the same population. The plants survive only in unstabilized blowouts where the sand is constantly shifting and there is little, if any, competing vegetation. Shinnersoseris rostrata was also discovered in a couple of neighboring dune areas in Sherburne County, but it is believed that these occurrences resulted from an old-field restoration effort using a seed mix from Nebraska, which could have contained seeds of this species. Shinnersoseris rostrata was listed as a threatened species in Minnesota in 1984.
Shinnersoseris rostrata is a distinctive plant that can be reliably identified in the field using nontechnical characteristics. It is a taprooted annual, 1-4 dm (4-16 in.) tall, with milky juice. Stems are smooth and green. Leaves are long and narrowly linear, the lower ones being opposite. Heads have 5 or more pink-colored flowers at the tips of long branches (Great Plains Flora Association 1986).
In Minnesota, S. rostrata has only been found on open sand dunes in a prairie landscape. Conditions are sunny and dry, becoming quite severe in late summer when heat and lack of water cause most species to shrivel and die. It occurs with another very rare species, Oryzopis hymenoides (Indian ricegrass), as well as the more common Sporobolus cryptandrus (sand dropseed), Cyperus spp. (umbrella sedges), Koeleria pyramidata (Junegrass), and Chrysopsis villosa (hairy golden aster).
Biology / Life History
Shinnersoseris rostrata is an insect-pollinated annual with a very distinct morphology. In fact, it has been moved to its own monotypic genus Shinnersoseris, following taxonomic research conducted by Tomb (1973). The species presumably depends on a persistent seed bank to maintain populations, and seed germination requires scarification in the form of physical abrasion. This is believed to happen as a result of the seed tumbling over the sand, or possibly by the sand blowing over the seed.
Conservation / Management
Shinnersoseris rostrata requires open, sparsely vegetated sand dunes. It will not survive long if the dunes become covered with vegetation. This is true whether the encroaching vegetation is comprised of trees and shrubs or of a dense cover of sod, even if the sod is comprised of native grass species. Maintaining open conditions must be the primary goal of habitat management. The use of prescribed fire may be helpful in reaching this goal, but it will probably need to be augmented by brush cutting, or in extreme cases, the judicious removal of herbaceous plants. This must be done with great care and planning. It is erroneous to assume that allowing an area of overgrown dunes to be used by off-road vehicles or grazed by animals to open up the dunes will create suitable habitat. Changes in the vegetation and fluctuations in the population of S. rostrata should be monitored regularly.
Conservation Efforts in Minnesota
Because the single site in Norman County and the three locations in adjacent Polk County are part of the same sand dune complex and considered a single population, this species needs close monitoring to ensure its longevity. Portions of the dune complex are in public ownership and are being managed as a natural area.
Great Plains Flora Association. 1986. Flora of the Great Plains. University Press of Kansas, Lawrence, Kansas. 1,402 pp.
Tomb, A. S. 1973. Shinnersoseris Gen. Nov. (Compositae: Chichorieae.) Sida 5:183-189.