Silphium laciniatum (Compass Plant)
|Also known as:|
|Habitat:||sun; dry to average sandy or loamy soil; prairies, glades, railroads, roadsides|
|Bloom season:||July - September|
|Plant height:||3 to 10 feet|
|Wetland Indicator Status:||none|
|MN county distribution (click map to enlarge):|
|National distribution (click map to enlarge):|
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Small clusters of stalked flowers at the top of the stem and arising singly or in small clusters from the upper leaf axils. Flowers are 2½ to 4 inches across with 17 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 flowers are sterile, yellow, tubular with 5 triangular lobes and a column of brown stamens with long, stringy style-like tips.
Bracts are in 2 or 3 layers, generally lance-shaped with a pointed tip that is often spreading. Bracts and flower stalks are densely covered in long, spreading, white hairs. Flower stalks are generally short on the lower stem and longer above.
Leaves and stems:
Leaves are deeply divided into linear-oblong lobes, pointed at the tips, densely covered in short hairs, and the edges toothless or with a few irregular teeth or smaller lobes. Basal leaves are erect, stalked or stalkless, 1 to 2 feet long and about half as wide.
Stem leaves become smaller and shorter stalked as they ascend the stem, the uppermost leaves reduced to bracts and typically unlobed. Stems are erect, unbranched except in the flowers, stout, and densely covered in long, spreading hairs.
Fruit is a dry, flat seed that forms from the ray flowers on the outer ring of the disk.
Compass Plant is easy to distinguish from other Silphium species in Minnesota from the deeply divided leaves and densely hairy bracts and stem. The common name comes from the tendency of basal leaves to orient themselves vertically in a north-south direction to avoid the full brunt of the sun.
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Photos by K. Chayka taken at Iron Horse Prairie SNA, Dodge County. Photos courtesy Peter M. Dziuk taken in Dodge County and in a private garden in Anoka County.
Have you seen this plant in Minnesota, or have any other comments about it?