Lycopus americanus

Native

Common. The most abundant species of the genus Lycopus.

Wet or moist. Marshes, wet meadows, fens, stream banks, ditches, lake shores.

July to September

White

4″ to 40″

This is a 4″ to 40″ tall, erect, perennial forb that rises from a long, horizontal rhizome and fibrous roots. The rhizome does not have tubers.

The stems are erect, branched or unbranched, green, square, hollow, and hairless except for tufts of hairs in the leaf axils. They are weak and may sprawl without nearby supportive vegetation. There is a single vertical groove on each side of the stem.

The leaves are opposite and variable in shape. Each pair of opposite leaves is at right angles to the leaf pairs above and below it. The leaf blades may be lance-shaped or narrowly oblong to nearly linear. They are 1⅛″ to 3⅛″ long and ¾″ to 2¾″ wide. They taper gradually at the base to a short leaf stalk and taper at the tip to a narrow point. The lower leaves are deeply and irregularly pinnately lobed near the base, deeply toothed near the tip, and short stalked. They become progressively less lobed, less deeply toothed, and shorter stalked as they ascend the stem. Upper leaves are coarsely toothed, unlobed, and stalkless. The upper surface is hairless. The lower surface is hairless except for short hairs along the veins. Although this is a mint, when crushed the leaves do not smell of mint.

The inflorescence is a tight cluster of 10 to 26 stalkless flowers in the leaf axils on the upper ⅔ of the stem. Pairs of clusters in opposite leaf axils form false whorls.

There are 5 green sepals (calyx) that are united for most of their length into a 1 ⁄16″ to ⅛″ long, bell-shaped tube with 5 teeth. The calyx teeth are 1 ⁄16″ to ⅛″ long, firm, sharply pointed, narrowly triangular, and more than twice as long as their base is wide. There are 5 white petals (corolla) that are united at the base into a tube that is barely longer than the calyx tube, and are separated at the tip into 4 spreading lobes. The upper lobe is notched at the tip and is broader than the lower and lateral lobes. The petals are sometimes spotted with pink or purple. There are 2 fertile stamens with brown anthers and 2 sterile stamens (staminodes). The stamens and the style are barely longer than the corolla tube. The staminodes are club-like and are shorter than the corolla tube. The flowers are not fragrant.

The fruit is a set of 4 egg-shaped, brown, hairless, ridged nutlets with one seed each. The inner angle is shorter than the outer ones so that the center of the nutlets is depressed. When the fruit is mature the calyx lobes surpass the nutlets.

See the Lycopus ID Filter for a spreadsheet to aid identification of this and similar species.

Northern bugleweed (Lycopus uniflorus var. uniflorus) produces a stolon with a tuber at the tip. The leaves are shorter and are not lobed. The calyx teeth are are shorter, no more than 1 ⁄32″ long. The corolla has 5 lobes, not 4. When the fruit is mature the nutlets surpass the calyx lobes.

Rough bugleweed (Lycopus asper) leaves are not lobed.

Sherard’s waterhorehound (Lycopus X sherardii) is a hybrid between northern bugleweed and Virginia bugleweed. It is found wherever the ranges of the two species overlap.

Virginia bugleweed (Lycopus virginicus) leaves are hairy on the underside and are not lobed. The calyx has 4 teeth, not 5. The calyx teeth are are shorter, no more than 1 ⁄32″ long. When the fruit is mature the nutlets surpass the calyx lobes.