Rare Species Guide

  Synonyms

Lygodesmia rostrata

  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 (annual skeletonweed) is extremely rare. Prior to 1986, the sole known occurrence was in Norman County. In 1986 it was discovered at two additional locations in adjacent Polk County, but all of the locations are part of the same population (Red River Prairie and Aspen Parklands subsections). 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 sand dune in Sherburne County, but that occurrence is believed to have 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.

  Description

Shinnersoseris rostrata is a distinctive plant that can be reliably identified in the field using nontechnical characters. It is an herbaceous taprooted annual, 1-4 dm (4-16 in.) tall, with milky juice. Stems are smooth, green, and have numerous long branches. The branches form a panicle with each bearing a flower head at the tip. Heads are narrowly cylindrical and have 8-11 pink-colored flowers. Leaves are all cauline; there is no basal rosette of leaves. They are long and linear, smooth with entire margins. The lower leaves are opposite, the upper ones are alternate (Tomb 1973).

  Habitat

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, Achnatherum hymenoides (Indian rice grass).

  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 domestic 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.

  Best Time to Search

The best time to search for Shinnersoseris rostrata is when in flower, from early July to the middle of August.

  Conservation Efforts in Minnesota

Because the single site in Norman County and the two 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 natural areas.

  Authors/Revisions

Welby R. Smith (MNDNR), 2021

(Note: all content ©MNDNR)

  References and Additional Information

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

The Great Plains Flora Association. 1986. Flora of the Great Plains. University Press of Kansas, Lawrence. 1,402 pp.

Tomb, A. S. 1973. Shinnersoseris Gen. Nov. (Compositae: Chichorieae.) SIDA 5:183-189.