Silphium integrfolium (Rosinweed)
|Also known as:||Whole-leaf Rosinweed, Prairie Rosinweed|
|Habitat:||part shade, sun; prairie, open woods, clearings|
|Bloom season:||July - September|
|Plant height:||3 to 6 feet|
|Wetland Indicator Status:||none|
|MN county distribution (click map to enlarge):|
|National distribution (click map to enlarge):|
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Clusters of stalked flowers at the tip of branching stems and arising from upper leaf axils. Flowers are 2 to 3 inches across with 12 to 35 yellow petals (ray flowers) that are fertile and have a split style protruding from the short tube at the base. The center disk is green until the disk flowers bloom; disk flowers are sterile, yellow, tubular with 5 triangular lobes and a column of brown stamens with long, stringy style-like tips.
Leaves and stems:
Basal leaves wither away by flowering time. Stem leaves are opposite, mostly ascending, up to 5 inches long and 2½ inches wide, egg to teardrop-shaped with a pointed tip and rounded base that is stalkless and somewhat clasps the stem, the edges toothless or with a few small teeth. Depending on the variety, surfaces are hairless, or rough on the upper surface and soft hairy on the lower. Stems are single or multiple from the base, erect, stout, branched in the upper plant, round to weakly 4-sided, and smooth or covered in short hairs.
Fruit is a dry, flat seed that forms from the ray flowers on the outer ring of the disk.
Rosinweed is a tall-grass prairie species whose natural range extends to Wisconsin and Iowa and does not quite reach Minnesota, but it is available in the nursery trade and may be included in prairie seed mixes and in restored plantings. There are 2 recognized varieties, var. integrifolium, the more common is hairy and var. laeve mostly hairless. Both are otherwise easily distinguished from the other Silphium species in Minnesota by the stalkless, egg to teardrop-shaped leaves.
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Photos by K. Chayka taken in a private garden in Washington County. Photos courtesy Peter M. Dziuk taken in a private garden in Anoka County.
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