Cuscuta glomerata (Rope Dodder)
|Also known as:||Aster Dodder|
|Family:||Convolvulaceae (Morning Glory)|
|Habitat:||part shade, sun; moist soil; prairies, sedge meadows, swamps|
|Bloom season:||July - September|
|Plant height:||3 to 4 foot vine|
|Wetland Indicator Status:||none|
|MN county distribution (click map to enlarge):|
|National distribution (click map to enlarge):|
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Dense rope-like coil of stalkless white flowers spiralling up the main stem of its host. Flowers are 1/8 inch long, with 5 fused petals, the lobes narrow lance-like, pointed at the tip, and spreading star-like to slightly curled back (reflexed). The 5 calyx lobes are long and narrowly triangular, as long as the floral tube, loose with tips reflexed; around the base of the calyx are 8 to 15, spreading to ascending, triangular bracts. In the center of the floral tube is the ovary with two elongated styles, each about as long as the ovary with a prominent round stigma at the tip (capitate); the ovary is swollen around the base of the styles creating a small ridge called a stylopodium. 5 yellow-tipped stamens extend out of the tube, and are attached to the petal below the base of the sinus between the petal lobes. Hidden inside the floral tube, surrounding the ovary, are fringed scales that barely reach the base of the stamens, typically shorter.
Leaves and stems:
Leaves are tiny and scale-like or absent altogether. Stems are hairless and slender, typically yellow to orange, forming wiry masses that twist around and are supported by the host plant. Along the stem are small appendages (haustoria), modified roots that penetrate the host plant and draw moisture and nutrients from it.
Fruit is a round but flattened (wider than tall) capsule, about 1/8 inch diameter, the dried stylopodium creating a thickened ridge around the opening at the tip of the capsule, from which the seeds are disseminated. Capsules are brown when mature.
Rope Dodder is one of nine Cuscuta species either present (6) or historically documented (3) in Minnesota. This is perhaps the mostly easily identifiable of all our native dodders by its dense, continuous rope-like mass of flowers, as well as the dense bracts around the base of each flower. While most dodders are associated with a broad host range, some are fairly specialized to only a few species and when those species are natives in a dwindling habitat, some of those dodder species can become rare. This is listed as a Special Concern species in Wisconsin. Cuscuta glomerata is noted as having a preference for members of the Aster family, often on Goldenrod, though some specimens found in the location where these images were taken were hosting on Virginia Mountain Mint. As to the pest potential of Rope Dodder, there is little to no reference to it as such in literature.
All dodders are obligate parasites, that is they must obtain all their life support from a host species to grow and reproduce. Dodders not only sap energy from their hosts but are also capable of moving diseases from one host to another. When a dodder seedling germinates, it must quickly contact a suitable host upon which it immediately begins to twine around the host plant's stem, invading its tissue via the haustoria, after which the initial seedling root quickly withers away. As the stems grow, they contact and invade more stems, even crossing over and connecting to other suitable host species. All species of dodder are on the federal noxious weed list, except some native species (including Minnesota's natives) as well as a few, now widespread non-native species. Still all dodders, including natives, are "regulated" requiring federal permits for importation or transportation of seed.
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Photos courtesy Brian O'Brien taken at Cedar Mountain SNA, Redwood County.
Have you seen this plant in Minnesota, or have any other comments about it?