Physaria ludoviciana (Nutt.) O'Kane & Al-Shehbaz
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Basis for Listing
A small perennial species, Physaria ludoviciana is characteristic of dry plains in the western United States. But it also occurs in Minnesota, where it is apparently restricted to dry, sand-gravel prairies and bedrock bluff prairies in the immediate vicinity of Red Wing in Goodhue County. In fact, most of the colonies actually occur within the city limits. Plants were discovered there in 1886 and have escaped urbanization because they occur on the steep bluffs, instead of in the valleys and bottomlands that have been extensively altered by human settlement. This remarkable population is disjunct 500 km (310 mi.) from the main range of the species. The origin of P. ludoviciana in Minnesota is uncertain, but it may have arrived at some point in the distant past through the long-range dispersal of a single seed. Or it could be a relict of a previous climatic period when the prairies occurred farther east than they do today. In any case, the existence of such an outlier population has special biological significance and provides genetic variability, which is thought to play a role in speciation.
Like all members of the mustard family, P. ludoviciana has 4 sepals, 4 petals, 6 stamens, and a fruit with 2 chambers. Distinguishing features include the yellow petals; the leaves, which are simple, narrow, form a basal rosette, and have soft, distinct, thin hairs; and the fruit, which is globe-shaped and has soft, thin hairs. Other species with which P. ludoviciana might be confused are western species not found in Minnesota.
In Minnesota, P. ludoviciana occurs in a dry prairie habitat on a series of south-facing bluffs. These are classified as bedrock bluff prairies and sand-gravel prairies. The plants appear to prefer exposed, sandy soils derived from weathered limestone.
Biology / Life History
Physaria ludoviciana is at the easternmost extent of its range in Minnesota, and the bulk of the populations occur at more southern latitudes. This may account for its affinity for south-facing slopes in this northern outpost. The species is avoided by grazing animals (Van Bruggen 1992) and exhibits polyploidy (Rollins and Shaw 1973).
Conservation / Management
Outlying populations often carry unique genetic traits, making them valuable to a species' survival. It is important to protect and to maintain the viability of the P. ludoviciana populations found in Minnesota. Continued monitoring of the populations is recommended. Although the sites are not at great risk of development or agriculture, they are at risk from encroachment of surrounding woodlands. The mechanical removal of encroaching shrubs followed by a carefully timed regimen of prescribed fire is recommended. Physaria ludoviciana plants are extremely vulnerable to fire once they have emerged from the ground, so prescribed burns should be conducted in very early spring before they emerge.
Conservation Efforts in Minnesota
A long-term monitoring project has been established for this species that is designed to provide answers to the challenges of habitat management.
Great Plains Flora Association. 1986. Flora of the Great Plains. University Press of Kansas, Lawrence, Kansas. 1,402 pp.
Larson, G. E. and J. R. Johnson. 1999. Plants of the Black Hills and Bear Lodge Mountains. South Dakota State University, Brookings, South Dakota. 608 pp.
Rollins, R. C., and E. A. Shaw. 1973. The Genus Lesquerella (Cruciferae) in North America. Harvard University Press, Cambridge, Massachusetts. 300 pp.
Smith, W. K., A. K. Knapp, J. A. Pearson, J. H. Varman, J. B. Yavitt, and D. R. Young. 1983. Influence of microclimate and growth form on plant temperatures of early spring species in a high-elevation prairie. The American Midland Naturalist 109(2):380-389.
Van Bruggen, T. 1992. Wildflowers, grasses, and other plants of the Northern Plains and Black Hills. Fourth Edition. Badlands Natural History Association, Interior, South Dakota. 107 pp.