Eupatorium altissimum (Tall Boneset)
|Also known as:||Tall Thoroughwort|
|Habitat:||part shade, sun; open woods, thickets, prairies, along railroads, waste areas|
|Bloom season:||August - September|
|Plant height:||2 to 6 feet|
|Wetland Indicator Status:||none|
|MN county distribution (click map to enlarge):|
|National distribution (click map to enlarge):|
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Flat-topped branching clusters of stalked flowers at the top of the stem and arising from upper leaf axils, a cluster comprised of numerous small clusters of 4 to 11 disk flowers each. Flowers are about 1/8 inch across, dull white, star-shaped with 5 triangular petal-like lobes. In the center is a brown column of white-tipped stamens; styles are white, flattened, long and string-like. The bracts around the base of a flower are in 2 or 3 layers, green with white edging, and hairy; the inner bracts are oblong and much longer than the outer bracts.
Leaves and stem:
Leaves are 2 to 5 inches long and to 1 inch across, minutely hairy, widest near or above the middle, pointed at the tip with a long taper to the base, and stalkless or nearly so. There are small, widely-spaced teeth in the tip half of leaves but smaller leaves in the upper part of the plant may be toothless. Leaves have 3 conspicuous parallel veins and there are often smaller leaves in the axils. Stems are erect, unbranched except near the flowers, minutely hairy, and green or tinged reddish brown.
While the flowers of Tall Boneset look much the same as those of Common Boneset (Eupatorium perfoliatum), the 2 species are easily distinguished by the leaves, with Common Boneset having opposite leaves that join around the stem. Common Boneset also prefers moist soil where Tall Boneset is found in medium moisture to dry habitats, and starts blooming later in the season. The flowers superficially resemble those of White Snakeroot (Ageratina altissima), which is a woodland species that has more heart-shaped leaves.
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Photos by K. Chayka taken along the railroad tracks at Long Lake Regional Park, Ramsey County.
Have you seen this plant in Minnesota, or have any other comments about it?