Basis for Listing
Orobanche ludoviciana (Louisiana broomrape) is common in the Great Plains but is very rare in Minnesota and in states further east. In Minnesota, it occurs in prairies and savannas, primarily in sandy soils or shallow stony soils over bedrock. Most of the known populations are associated with sand dunes and beach ridges on the shores of historic Glacial Lake Agassiz in northwest Minnesota (Red River Valley Section) and with deep sand deposits along the Minnesota, St. Croix, and Mississippi rivers (North Central Glaciated Plains, Minnesota & NE Iowa Morainal, and Paleozoic Plateau sections). Since over 99% of the prairie, and savanna habitat that was present in the state before settlement has been lost (Minnesota's Remaining Native Prairie), there is a limited amount of potential habitat remaining for this species in Minnesota. In addition, the plant is an obligate root parasite that lacks chlorophyll, and consequently it is limited to sites where suitable host plants are present. The fragmented habitat remnants in which O. ludoviciana occurs are susceptible to invasion by non-native species, sand and gravel quarrying exploits, energy production ventures, and the expansion of residential developments. For these reasons, O. ludoviciana was designated special concern in 1984. A lack of systematic field surveys prevented it from being assigned a more protective status. Since then, systematic surveys have been completed by the Minnesota Biological Survey, which revealed O. ludoviciana to be even rarer than previously thought. It was also determined that habitat conditions had significantly deteriorated since 1984. Based on this evidence, the status of O. ludoviciana was elevated to threatened in 2013.
There are three species of Orobanche (broomrapes) in Minnesota. All are herbaceous annuals that lack leaves and green pigmentation (chlorophyll), and the stems of the plants are primarily subterranean. In two of the species, O. fasciculata (clustered broomrape) and O. uniflora (one-flowered broomrape), all that is seen aboveground are the flower stalks (pedicels), with a single flower at the end of each. It looks as if each flower is coming out of the ground individually.
In the case of O. ludoviciana, all the flowers appear to be attached to an upright above-ground stem. They are packed tightly together to form a dense spike. This species looks quite different from the others and should be easy to identify. Orobanche ludoviciana is often easier to see after it dies, as it dries to a rather conspicuous dark-brown color. These dead plants usually persist through winter to the following spring, when they are still easy to spot.
Orobanche ludoviciana occurs in habitats classified as northern dry prairie and southern dry prairie (including dunes), and in northern dry savanna and southern dry savanna, particularly in areas with excessively drained, loose and sandy or gravelly soil. These habitats tend to have sparse vegetation dominated by grasses and well drained (droughty) soils. Habitats are not always pristine natural areas, though they seem to be dominated by native prairie species even though species diversity may be low. Typical associates include Artemisia spp. (wormwood species), Heterotheca villosa (hairy golden aster), Liatris punctata var. punctata (dotted blazing star), Bouteloua gracilis (blue grama), and other dry prairie species. The rare O. fasciculata has been found with O. ludoviciana at a few sites.
Biology / Life History
Orobanche ludoviciana is an annual vascular plant that lacks true leaves and green pigmentation (chlorophyll) and is incapable of photosynthesis. Instead, it is obligately parasitic on the roots of other vascular plants (hosts) to obtain the carbohydrates needed to sustain it. Across its range, O. ludoviciana uses perennial members of Asteraceae (Composite family) as hosts, including Grindelia squarrosa (curly cup gumweed), Heterotheca spp. (golden asters), and Artemisia spp. and occasionally other genera (Collins et al. 2009). The most frequent host plants noted in Minnesota are Artemisia frigida (sage wormwood) and A. campestris ssp. caudata (field sagewort), but Heterotheca villosa has also been reported. The plant produces insect-pollinated flowers and reproduces exclusively by seed. Seeds are minute and are shed from dried capsules.
Conservation / Management
Many of the known O. ludoviciana populations are quite small, and the fragmented habitat remnants in which they occur are susceptible to invasion by non-native species, sand and gravel quarrying ventures, development, and some recreational activities. The status of O. ludoviciana as a parasitic species does not imply any specific management or conservation needs. However, because it likely restricts the species to habitats where host plants have large and healthy populations, it's even more important to maintain the health of the whole community of plants in which it lives. This can be accomplished by periodic dormant-season burns to eliminate woody encroachment, control of exotic species, and exclusion of motorized vehicles and domestic livestock.
Several programs and resources are available to land managers and landowners to help protect and manage remaining prairie parcels, including the Native Prairie Bank Program, the Native Prairie Tax Exemption Program, and a prairie restoration handbook.
Best Time to Search
Orobanche ludoviciana can be seen and identified anytime it is above ground. In Minnesota it has been observed as early as late May and as late as late September. However, most recorded observations in Minnesota are from late-July through the end of August, and this may be the best time to search for this plant.
Conservation Efforts in Minnesota
About one-third of the recorded populations of O. ludoviciana are in sites that are owned by public land management agencies and private conservation groups. Some, perhaps most, of these sites are actively managed in some way, though goals and objectives vary. Unfortunately the effects of various management activities on O. ludoviciana are not being monitored.
Welby Smith (MNDNR), 2008 and 2018
(Note: all content ©MNDNR)
References and Additional Information
Coffin, B., and L. Pfannmuller, editors. 1988. Minnesota's endangered flora and fauna. University of Minnesota Press, Minneapolis. 473 pp.
Collins, L. T. 1973. Systematics of Orobanche section Myzorrhiza (Orobanchaceae) with emphasis on Orobanche ludoviciana. Thesis, University of Wisconsin, Milwaukee, Wisconsin.
Collins, L. T., A. E. L. Colwell, and G. Yatskievych. 2009. Orobanche riparia (Orobanchaceae), a new species from the American Midwest. Journal of the Botanical Research Institute of Texas 3(1):3-11.
Kuijt, F. 1969. The biology of parasitic plants. University of California Press, Berkeley, California. 246 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.
Minnesota Department of Natural Resources. 2006. Tomorrow's habitat for the wild and rare: An action plan for Minnesota wildlife, comprehensive wildlife conservation strategy. Division of Ecological Services, Minnesota Department of Natural Resources. 297 pp. + appendices.
Minnesota Department of Natural Resources. 2009. Map of Minnesota's remaining native prairie 100 years after the public land survey.
Robert W. Freckmann Herbarium, University of Wisconsin-Stevens Point. 2010. Wisconsin Plants web site: Orobanche ludoviciana.
The Great Plains Flora Association. 1986. Flora of the Great Plains. University Press of Kansas, Lawrence. 1,402 pp.
Thieret, J. W. 1971. The genera of Orobanchaceae in the southeastern United States. Journal of the Arnold Arboretum 52:404-434.