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Lycopus americanus Muhl. ex W.P.C. Barton

American water-horehound

KingdomPlantaePlants, but not fungi, lichens, or algae
SubkingdomTracheobiontaVascular plants—plants with a “circulatory system” for delivering water and nutrients
DivisionMagnoliophytaFlowering plants, also known as angiosperms
ClassMagnoliopsidaDicotyledons—plants with two initial seed leaves
SubclassAsteridaeA large class that encompasses asters
OrderLamialesAromatic herbs and shrubs, including lavender, lilac, olive, jasmine, ash, teak, snapdragon, sesame, psyllium, garden sage, mint, basil, and rosemary
FamilyLamiaceaeMint family
GenusLycopusFrom the Greek lykos, “wolf,” and pous, “foot”
SpeciesamericanusAmerican

About plant names...

American water-horehound is a North American native. It prefers lake and river shores, and wetland edges.

Plants: 1-3′ (30-91 cm) tall, unbranched or sparingly branched, sometimes sprawling. The main stem is four-angled and ridged, and hairless or nearly so.

Leaves: Lower leaves are deeply lobed, and up to 3½″ (8.9 cm) long × 1½″ (3.8 cm) wide. Leaves are narrowly oval, narrowly oblong, or linear. They are opposite, becoming smaller near the top, and coarsely toothed. Upper leaf surfaces are typically hairless.

Flowers: In small clusters at leaf axils. Individual flowers are ⅛″ (3.2 mm) in size, and white, with tiny purplish spots. They are tubular in shape, emerging in all directions from leaf axils.

Fruits: Nutlets are in groups of four, together forming a square shape. Each is 1/32-1/16″ (1.2-1.7 mm) long.

Members of Lycopus, the water-horehounds, are notor­iously hard to distinguish. They are also easily confused with some members of other genera. Here are some comparisons.

 

Lycopus americanus (American water-horehound)

9/2/2017 · Rocky Ridge Trail, Beaver Brook Conservation Area, Hollis, New Hamp­shire · ≈ 4½ × 7″ (12 × 18 cm)

Lycopus americanus (American water-horehound)

8/18/2010 · J. Harry Rich Woods, off Nod Rd., Groton, Mass­a­chu­setts · ≈ 5 × 8″ (13 × 19 cm)

Lycopus americanus (American water-horehound)

8/18/2010 · J. Harry Rich Woods, off Nod Rd., Groton, Mass­a­chu­setts · ≈ 11 × 7″ (27 × 18 cm) ID is uncertain

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Lycopus americanus

Lycopus uniflorus

Lycopus virginicus
Common Name

American water-horehound

northern bugleweed

Virginia water horehound
Plant 1-3′ (30-91 cm) tall, unbranched or sparingly branched, sometimes sprawling. The main stem is four-angled and ridged, and hairless or nearly so. 4-20″ (10-50 cm) tall, usually straight or with a few branches. Stems are four-angled and almost hairless. 1-3′ (38-91 cm) tall, with an unbranched stem. It is erect, or sometimes leaning. Stems are roughly square in cross-section, and covered with fine hairs which may point outward or lie flat against the stem (appressed). These plants often (but not always) lack the thick tuberous roots of other water-horehounds.
Flowers In small clusters at leaf axils. Individual flowers are ⅛″ (3.2 mm) in size, and white, with tiny purplish spots. They are tubular in shape, emerging in all directions from leaf axils. Flowers occur in dense clusters at leaf axils. They are tubular, reaching in every direction from the leaf axil, and about ⅛″ (3.2 mm) around at the end. Flowers appear in tight clusters at leaf axils. They are tubular in shape, and each is about ⅜″ (1 cm) long × ⅛″ (3.2 mm) in diameter. They emerge in all directions from the axil. Flowers are white, with a few pink spots.
Leaves Lower leaves are deeply lobed, and up to 3½″ (8.9 cm) long × 1½″ (3.8 cm) wide. Leaves are narrowly oval, narrowly oblong, or linear. They are opposite, becoming smaller near the top, and coarsely toothed. Upper leaf surfaces are typically hairless. Up to 3″ (7.6 cm) long × 1″ (2.5 cm) wide. They are hairless or nearly so, with 2-7 teeth on each side of the leaf. The leaves are opposite, and each pair are rotated 90° from the previous pair. 1-4½″ (3-12 cm) × ⅜-1¾″ (1-5 cm). Oval or lanceolate, unlobed, with coarsely toothed edges. The lowest teeth are a little below the mid-point of each leaf. Leaves are more egg-shaped than those other water-horehounds. Leaves are dark green or purple, and opposite. Leaves nearer the bottom have a short stalk, while those near the top are attached almost directly to the stem. Upper leaf surfaces are nearly hairless, while lower surfaces have a hairy central vein and may have fine hairs elsewhere.
Fruit Nutlets are in groups of four, together forming a square shape. Each is 1/32-1/16″ (1.2-1.7 mm) long. Nutlets are 1/32-1/16″ (1-2 mm), in groups of four. Each flower is replaced by four small nutlets, packed in roughly the shape of a square. Nutlets are 1/32-1/16″ (1.3-2 mm) × ~1/32″ (0.7-1.3 mm).
Range/ Zones

USDA Zones: 4-8

Habitats Lake and river shores, and wetland edges. Wet areas such shores, swamps, marshes, wet meadows, and stream banks. River banks, floodplains, wet meadows, clearings, and shores.
Type Wild Wild Wild
Occurrence      

 

 
Leonurus cardiaca
Common Name

motherwort
Plant 2-3′ (60-100 cm) high. The stems are square in cross-section. Their preference for dryer habitats distinguishes them from water horehounds.
Flowers Between each pair of leaves, a tuft of small pink-purple flowers appear directly on the stem, becoming more closely spaced near the top
Leaves Leaves are opposite. Pairs of leaves extend from the stem every inch or so, in alternating directions exactly at right angles to each other, looking almost unnaturally orderly. Leaves are dark green, and are 2-4″ (5-10 cm) long. Younger leaves have three pointed tips, while older ones are further divided.

Fruit Each flower becomes 4 reddish brown or brown nutlets. Each nutlet is 3-sided.
Range/ Zones

Habitats Woodland borders, disturbed open woodlands, and partially shaded yard edges.
Type Wild
Occurrence Common

 

Online References:

Illinois Wildflowers

Minnesota Wildflowers

Michiganflora.net

Gobotany.nativeplanttrust.org

References:

Clemants, Steven; Gracie, Carol, Wildflowers in the Field and Forest, Oxford University Press, 2006, p. 342

Weakley, Alan S.; Ludwig, J. Christopher; Townsend, John F.; Crowder, Bland (Ed.), Flora of Virginia, Botanical Research Institute of Texas Press, 2013, p. 667

Lycopus americanus (American water-horehound)

9/11/2013 · Nashua River Rail Trail, Groton Center, Groton, Mass­a­chu­setts · ≈ 6 × 9″ (15 × 22 cm) ID is uncertain

Lycopus americanus (American water-horehound)

8/18/2010 · J. Harry Rich Woods, off Nod Rd., Groton, Mass­a­chu­setts · ≈ 6 × 9″ (15 × 23 cm)

Lycopus americanus (American water-horehound)

9/3/2020 · Mitchell Field, Harpswell, Maine · ≈ 4 × 6″ (11 × 16 cm)

Lycopus americanus Muhl. ex W.P.C. Barton var. longii Benner

Lycopus americanus Muhl. ex W.P.C. Barton var. scabrifolius Fernald

Lycopus sinuatus Elliott

 

Lycopus americanus description by Thomas H. Kent, last updated 16 Sep 2020.

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Lycopus americanus (American water-horehound)

9/3/2020 · Mitchell Field, Harpswell, Maine · ≈ 4 × 6″ (10 × 15 cm)

Lycopus americanus (American water-horehound)

9/2/2017 · Rocky Ridge Trail, Beaver Brook Conservation Area, Hollis, New Hamp­shire · ≈ 4½ × 7″ (12 × 18 cm)

Range:

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