Rare Species Guide

  Synonyms

Lesquerella ludoviciana

  Basis for Listing

Physaria ludoviciana (bladderpod) is a small perennial plant characteristic of dry sand prairies and sand dunes 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 (The Blufflands Subsection). 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. There is also one isolated population in Illinois and one in Wisconsin; it is listed as endangered in both states. 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.

Physaria ludoviciana is currently established on at least four discrete bluffs and does not appear to be directly threatened by human activities. However, profound changes are occurring in its habitat as a consequence of fire suppression. In the absence of natural prairie fires, trees and shrubs are invading the prairie bluffs and the amount of open grassland habitat is diminishing. Active management is needed to reverse this trend. Physaria ludoviciana was listed as an endangered species in Minnesota in 1984.

  Description

Physaria ludoviciana is a rather small plant, standing 10-35 cm (4-14 in.) tall. Like all members of the mustard family, it has 4 sepals, 4 petals, 6 stamens, and a fruit with 2 chambers. The flowers are yellow, 7-9 mm (0.3-0.4 in.) across and clustered at the top of the plant. When at their peak, the flowers are usually obvious. The leaves are simple, narrow, 2-6 cm (0.8-2.4 in.) long with entire margins. They occur along the length of the stem and also form a basal rosette. The fruit is a small dry spherical structure 4-6 mm (0.2 in.) across. The entire plant is covered with silvery hairs and is often given the common name “silvery bladderpod”.

  Habitat

In Minnesota, P. ludoviciana occurs in a dry prairie habitat on a series of south-facing bluffs. These are classified as dry bedrock bluff prairies and dry sand-gravel prairies. The plants appear to prefer exposed sandy soils derived from weathered limestone.

  Biology / Life History

Physaria ludoviciana is a short-lived perennial forb of the mustard family. It flowers very early in the spring and sheds seeds in June and July. The flowers are pollinated by a variety of small flying insects. Flowers that are self-pollinated fail to produce seeds (Claerbout et al. 2007), indicating self-incompatibility. A study in Illinois found seed production to be 110-744 seeds per reproductive plant (Grant et al. 2012). The seeds have no specialized mechanisms for long-range dispersal and do not regularly disperse far from the mother plant. One study in Illinois (Grant et al. 2012) failed to find a seed bank of P. ludoviciana in soil collected near reproductive plants, indicating that nearly all seeds germinate the year they were produced or were possibly lost to granivores, such as rodents or insects. Apparently seeds do not require cold stratification or scarification to germinate.

  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.

  Best Time to Search

The best time to search for Physaria ludoviciana is probably when flowering, from early May until mid-June. Specimens can also be identified when fruiting in June but become more difficult to find after the seeds have been shed and competing vegetation has grown taller.

  Authors/Revisions

Welby R. Smith (MNDNR), 2021

(Note: all content ©MNDNR)

  References and Additional Information

Claerbout, A. E., J. M. Coons, H. R. Owen, and K. R. Robertson. 2007. Floral biology of Physaria ludoviciana (Brassicaceae), a plant rare to the Midwest. Castanea 72(3):130-137.

Grant, M. C., A. E. Claerbout, J. M. Coons, and H. R. Owen. 2012. Seed biology of Physaria ludoviciana (silvery bladderpod; Brassicaceae), an endangered species in sand prairies of the Midwest. Journal of the Torrey Botanical Society 139(1):63-75.

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.

O?Kane, S. L., Jr. 2010. Physaria. Pages 616-665 in Flora of North America Editorial Committee, editors. Flora of North America north of Mexico. Volume 7. Oxford University Press, New York, New York.

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.