Chaiturus marrubiastrum (False Motherwort)
|Also known as:||Horehound Motherwort|
|Habitat:||part shade, sun; disturbed soil; lawns, woods, stream banks, fields, roadsides, waste places|
|Bloom season:||July - October|
|Plant height:||1 to 3 feet|
|Wetland Indicator Status:||none|
|MN county distribution (click map to enlarge):|
|National distribution (click map to enlarge):|
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Dense clusters of stalkless flowers surround the stem at the leaf nodes in the upper half or more of the plant and along branching stems. Usually only a few flowers in a cluster are open at the same time.
Flowers are pale pink to lavender to whitish, tubular, about ¼ inch long. The upper lip extends out like a hood, its outer surface covered in short, white hairs. The lower lip is 3-lobed with the center lobe largest; there are usually a few reddish-purple spots near the mouth of the tube. Purple stamens and a white style arch along the inside of the upper lip.The calyx is green, minutely hairy, about as long as the floral tube, and has 5 sharply pointed lobes with spiny tips.
Leaves and stems:
Leaves are opposite, finely hairy, and vary in size and shape as they ascend the stem. The lower leaves are up to 3½ inches long, nearly round to egg-shaped, bluntly pointed at the tip, coarsely toothed, on stalks up to about ¾ inch long. Leaves become more lance-elliptic as they ascend the stem, the uppermost leaves often with just a few teeth near the tip. Stems are square, variously hairy, usually branched. Plants create colonies from spreading rhizomes.
False Motherwort, formerly Leonurus marrubiastrum, is a Eurasian introduction that is not known to be widespread in Minnesota, but we suspect it is probably under-reported like many other weeds. The first report was in Anoka County in 1998, the second 10 years later in Goodhue County, then not again until 2021 when the subject came up in a Facebook group, where it was reported to be widespread in southeastern South Dakota. That triggered additional Minnesota sightings, in Hubbard and Hennepin counties. Our images came from the Hennepin County site, at Green Circle Park in Minnetonka.
False Motherwort resembles the much more common Motherwort (Leonurus cardiaca), which has lobed, maple-like leaves and its flowers have long hairs on the outer surface and a narrow, folded lower lobe. Also similar is the native Wild Mint (Mentha arvensis, a.k.a. M. canadensis), which has leaves more uniform in size and shape that are wonderfully aromatic when crushed.
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Photos by K. Chayka taken in Hennepin County.
Have you seen this plant in Minnesota, or have any other comments about it?