Lycopus americanus (American Water Horehound)

Plant Info
Also known as: American Bugleweed, Cut-leaved Bugleweed
Genus:Lycopus
Family:Lamiaceae (Mint)
Life cycle:perennial
Origin:native
Habitat:part shade, sun; moist soil; along shores, wet meadows
Bloom season:July - September
Plant height:6 to 30 inches
Wetland Indicator Status:GP: OBL MW: OBL NCNE: OBL
MN county distribution (click map to enlarge):Minnesota county distribution map
National distribution (click map to enlarge):National distribution map

Pick an image for a larger view. See the glossary for icon descriptions.

Detailed Information

Flower: Flower shape: 4-petals Flower shape: tubular Cluster type: whorled

[photo of flowers] A small dense cluster of 1/8-inch white flowers surrounds leaf axils along much of the stem, blooming from the bottom of the plant up and usually not all flowers in a cluster are open at the same time. Individual flowers are tubular, with 4 spreading lobes about equal in size. There are often tiny pinkish purple spots on the inside of the petals. 2 purple-tipped stamens extend out of the tube. The calyx is hairless, has 5 narrowly triangular lobes each with a sharply pointed tip and is about as long as the floral tube.

Leaves and stem: Leaf attachment: opposite Leaf type: lobed Leaf type: simple

[photo of leaves] The lower leaves are deeply lobed, up to 3½ inches long and 1½ inches wide, with a few scattered hairs along major veins on the underside, and little or no stalk. Leaves are progressively smaller as they ascend the stem and become coarsely toothed to nearly toothless at the top of the plant. The stem is square, mostly hairless, and unbranched.

Fruit: Fruit type: seed without plume

[photo of fruit] Fruit is a set of 4 nutlets forming a square, each nutlet containing a single seed. The calyx lobes are much longer than the fruits.

Notes:

There are several Lycopus species in Minnesota, all with similar clusters of small, white, tubular flowers at the leaf axils, most growing in the same type of habitat at the same time, often next to each other. American Water Horehound is most easily distinguished by its deeply lobed lower leaves, which the others all lack. Northern Bugleweed (Lycopus uniflorus) is otherwise distinguished by its short calyx, the lobes not exceeding the fruits; Rough Bugleweed (Lycopus asper) by its (usually) hairy stem and calyx; Virginia Bugleweed (Lycopus virginicus) by its broader, hairier leaves, stamens not extending out of the floral tube, and short calyx. Wild Mint (Mentha arvensis) also has clusters of small flowers in the axils, but it has usually pink to lavender flowers, and a strong mint scent when leaves are crushed. Lycopus species are not aromatic.

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More photos

Photos by K. Chayka taken in Ramsey County. Photos courtesy Peter M. Dziuk taken in Anoka County.

Comments

Have you seen this plant in Minnesota, or have any other comments about it?

Posted by: Kenny h - Shooting Star Trail West of Rose Creek
on: 2017-07-26 17:10:59

First time photo and ID on American Water Horehound...it flowers just like Motherwort...easy plant to ID this time...I will have to go back and check for the square stem

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