Orobanche uniflora (One-flowered Broomrape)
|Also known as:||Naked Broomrape, One-flowered Cancer-root|
|Habitat:||part shade, sun; sandy or rocky soil; prairies, savannas, along railroads, dunes, woods, bluffs|
|Bloom season:||June - August|
|Plant height:||3 to 9 inches|
|Wetland Indicator Status:||GP: UPL MW: UPL NCNE: UPL|
|MN county distribution (click map to enlarge):|
|National distribution (click map to enlarge):|
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Single flowers held nearly at a right angle at the tip of a leafless stalk, with up to 5 stalks arising from a (mostly) underground stem. Flowers are tubular and slightly curved, about ¾ inch long, white to violet to deep purple with 5 spreading oval lobes; the 2 upper lobes sometimes slightly larger than the lower 3. On either side of the bottom lobe and connected to the adjacent lobes is a small fold, typically colored bright yellow to orange. 4 stamens hug the inside of the upper tube.
The calyx cupping the flower is less than half the length of the floral tube, with 5 sharply pointed, narrowly triangular lobes about as long as or a little longer than the calyx tube. The flower lobe surfaces, stalks, and outer surfaces of the floral tube and calyx are covered with sticky glandular hairs.
Leaves and stems:
The stems are thick, all or mostly underground, typically less than 1 inch long with several lance-oval scales around the base of the emergent flower stalks. Stems, scales and flower stalks are typically grayish-tan, sometimes purplish. Plants may grow in small colonies, sometimes with 50 or more flowering stalks in a tight group.
Fruit is a 2-sectioned capsule, containing many seeds.
In Minnesota, Orobanche uniflora is a diminutive species of moist woodlands and open goat prairies. A plant without chlorophyll, it is an obligate parasite, completely dependent on a host plant for its moisture and carbohydrates to grow and reproduce, hosting on members of the Aster family as well as Sedum and Saxifrage, and perhaps others. While the most widespread of its genus in North America, ranging from coast to coast and Canada to Texas, it is very rare throughout most of the Upper Midwest, including Minnesota. Woodland invasive species such as buckthorn and garlic mustard will undoubtedly imperil it further. The Minnesota DNR listed it as a Special Concern species in 1984, elevating it to Threatened in 2013. Of note is that plants in the eastern part of its range, including Minnesota populations, apparently tend to have pale flowers, with deeper purple flowers more common in western populations. At least one reference notes this as var. purpurea and Tropicos lists a surprisingly large number of varieties, though they are not universally recognized. Most similar is the related Clustered Broomrape (Orobanche fasciculata), which has (mostly) above ground stems with a cluster of up to 12 flowers, their stalks about as long as the stem (including the underground portion).
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- One-flowered Broomrape plants
- a small colony of One-flowered Broomrape
- One-flowered Broomrape habitat, hosting on Solidago
- close-up of hairs on flower inner surface
- One-flowered Broomrape from Michigan
- western, purple, One-flowered Broomrape, hosting on Sedum
- rocky habitat
Photos courtesy Peter M. Dziuk taken in Lakeville, Dakota County, and on the Olympic Penninsula in Washington state. Photo courtesy Jeff Ausmus taken in Michigan.
Have you seen this plant in Minnesota, or have any other comments about it?