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Whorled Rosinweed

Species

Common Name Whorled Rosinweed

Latin Name: Silphium asteriscus var. Trifoliatum

[Pronounced: "SILPH-ee-um aster-ISS-cuss variety try-foh-lee-ATE-um"]

Formerly, and until recently, Silphium trifoliatum.

Type of Plant: Prairie Forb ("wildflower")


Identification Helps: Whorled rosinweed has leaves attached to the stems in a "whorl," as shown in the picture. It grows from 4 to 6 ft, with flowers appearing in late July through early September.


Similar Species: No other Ohio plant looks like whorled rosinweed. In the prairies to the west, commonly in Indiana, Illinois, and Wisconsin, common rosinweed, Silphium integrifolium, is a frequent, similar prairie plant. Rosinweed is not native to Ohio and should not be used in Ohio prairie restorations.


Recently, it has been determined that Ohio's whorled rosinweed is not so closely related to the common rosinweed, S. integrifolium to the west. Instead, it is, in fact, a unique northern variety of Silphium asteriscus, starry rosinweed, a plant in the states to the south of Ohio, including Kentucky and Tennessee. Our plant is now Silphium asteriscus var. trifoliatum, retaining the common name whorled rosinweed.


Preferred Growing Conditions in the Wild: Whorled rosinweed grows in a number of Ohio prairie environments, from slumping prairie stream banks, hillsides, and flat open prairie sites. This showy plant grows well in gardens and prairie restorations, but it can take several years to mature when planted as seeds.


The plant appears to grow naturally only on former or existing prairies. It does not spread into non-prairie areas.


Seasons of Growth and Bloom: The species blooms from July through September.

 

Natural Distribution in Ohio: Whorled rosinweed is found in all Ohio prairie regions.

 

Description and General Information: The plant is bold when in bloom, with a mass of 2-inch sunflower-like blooms at the top of the plant, as shown in the picture above. Before blooming, the plant can be identified by the whorled (meaning "ringed") arrangement of the leaves along the stem. At most nodes (points of attachment), three leaves are found. At some lower nodes, four or more leaves may be attached.