Orobanche fasciculata Nutt.
Basis for Listing
Only a small number of isolated colonies of Orobanche fasciculata (clustered broomrape) have been found in Minnesota. They are scattered in prairies in southeastern and western Minnesota (Eastern Broadleaf Forest and Prairie Parkland provinces), with perhaps the greatest concentration in the northwestern counties (Tallgrass Aspen Parklands). While the microhabitats of this species occur in sandy and gravelly prairies and were likely always uncommon, they have declined and become even more vulnerable since settlers first arrived in the state. In fact, less than 1% of Minnesota's original prairie habitat survives, and most are fragmented remnants. These remnants face numerous threats, particularly invasion by non-native species, sand and gravel quarrying, economic pressures to utilize grasslands for energy production, livestock grazing, and the expansion of residential developments. These were some of the justifications for listing O. fasciculata as special concern in Minnesota in 1984. Since that time, the Minnesota Biological Survey completed a comprehensive inventory of all the northwestern and southeastern counties within the species’ suspected range. When the status of O. fasciculata was reviewed in 2013, this newer data revealed O. fasciculata to be even more rare than previously thought and threats to its habitat even greater. For these reasons, the status of O. fasciculata 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 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 third species, O. ludoviciana (Louisiana broomrape), 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.
In order to distinguish O. fasciculata from O. uniflora, it may be necessary to gently remove some soil from the base of the plant. In both cases you will see the top of the underground stem, or at least the top of one branch of the stem. It will be vertical, and all the flowers will appear to come from there. At the point where each flower stalk is attached to the stem is a firm bract, which will look like a small stiff leaf. In the case of O. uniflora, the bracts are hairless, there will be only 1-3 flowers from each branch of the stem, and the flowers will be violet-tinged. In the case of O. fasciculata, the bracts are hairy, there will likely be 3-10 flowers from each branch, and the flowers will be pinkish to creamy-white.
Orobanche fasciculata occurs in dry prairies and dunes and savannas, particularly in excessively drained, loose, sandy or gravelly soil or in thin soil over bedrock. In the Prairie Parklands and Tallgrass Aspen Parklands provinces of northwestern Minnesota, it occurrs in northern dry prairie. In the Blufflands, it is often localized in southern dry prairie immediately downslope from sandstone outcrops. It does not seem to do well where there is a dense sod of rhizomatous grasses or in soil that has been previously plowed.
Biology / Life History
Orobanche fasciculata is a non-photosynthetic vascular plant that is parasitic on the roots of other vascular plants. Without its host plant it cannot produce carbohydrates in sufficient quantity to sustain itself. Species of the genus Artemisia (wormwood) appear to be its preferred host. Orobanche fasciculata produces insect-pollinated flowers like autotrophic species and reproduces exclusively by seed. The seeds are minute and are shed from dried capsules during the winter. Although all members of the genus Orobanche are considered to be annuals (Kuijt 1969), the actual life span of individuals of O. fasciculata has not been conclusively determined. It does appear that the species is monocarpic (Reuter 1986), which means that each individual dies after flowering. This may explain, in part, why the number of individuals in established populations is known to fluctuate greatly from year to year (Reuter 1986).
Conservation / Management
The status of O. fasciculata as a parasitic species does not imply any specific management or conservation needs; however, it may make it 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 fasciculata can be seen and identified anytime it is above ground, which is most reliably from early June through September.
Conservation Efforts in Minnesota
Several of the prairie habitats where O. fasciculata occurs are on public land that is being managed for conservation purposes.
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.
Higman, P. J., and M. R. Penskar. 1996. Special plant abstract for Orobanche fasciculata (fascicled broomrape). Michigan Natural Features Inventory, Lansing, Michigan.
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. 2005. Field guide to the native plant communities of Minnesota: the prairie parkland and tallgrass aspen parklands provinces. Ecological Land Classification Program, Minnesota County Biological Survey, and Natural Heritage and Nongame Research Program. Minnesota Department of Natural Resources, St. Paul, Minnesota. 362 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.
Minnesota Department of Natural Resources, Division of Ecological Resources. 2008. Rare species guide: an online encyclopedia of Minnesota's rare native plants and animals [Web Application]. Minnesota Department of Natural Resources, St. Paul, Minnesota. Accessed 1 July 2009.
Reuter, B. C. 1986. The habitat, reproductive ecology and host relations of Orobanche fasciculata Nutt. (Orobanchaceae) in Wisconsin. Bulletin of the Torrey Botanical Club 113:110-117.
Thieret, J. W. 1971. The genera of Orobanchaceae in the southeastern United States. Journal of the Arnold Arboretum 52:404-434.