Ohio Perennial and Biennial Weed Guide

Family:

Sunflower Family (Asteraceae)

Other Names:

chrysanthemum weed, common mugwort, felon herb, mugwort wormwood, St. John's plant, wormwood.

Origin and Distribution:

Mugwort was introduced from Europe into North America where it spread throughout northeastern U.S., into southern Canada, and along the Pacific Coast from Washington to central California. In Ohio, mugwort is well-established in a dozen eastern and southern counties. It is found growing in turfgrass, landscapes, waste places, shores, roadsides, and along railroads. The plant frequently establishes in sandy, open ground and prefers lime-rich soils.

Plant Description:

Mugwort is one of several closely-related herbs with an erect growth form and dissected leaves that generally give off a strong odor. Mugwort can be distinguished by its dark-green leaves, which are hairless above and silvery-white beneath due to a covering of wooly hairs, and its sage-like odor. Also, it has inconspicuous flower clusters on upright branches located at leaf axils on the upper portion of the stem. New plants arise at the upturned ends of short, stout, horizontal rhizomes (horizontal underground stems). The plant rarely reproduces from seeds.

• Root System:

  The root system is a mass of short, stout, horizontal, branched rhizomes (horizontal underground stems) from which adventitious roots are produced.

• Seedlings and Shoots:

  Young leaves are opposite (2 leaves per node), rounded, unlobed, bristly-hairy, wooly underneath, and attached to the stem by way of a long leaf stalk (petiole). Often, the edges of young leaves are conspicuously toothed. Young shoots sprouting from rhizomes are erect, gray-green, and resemble chrysanthemums.

• Stems:

  The erect stems are 2 to 6 feet tall and angular with longitudinal ridges or grooves and they become woody over time. Color ranges from green to green with purple ridges to entirely purple. Although stems are unbranched below, the upper part usually has branches. As many as 20 stems may emerge from the same root system.

• Leaves:

  Leaves are alternate (1 leaf per node) with a smooth, dark green upper surface and a lower surface that appears silvery due to white-wooly hairs. Leaves on the lower part of the stem are divided into 3 or 4 unequal, pointed lobes with coarsely-toothed edges that are divided into even smaller segments. Lower leaves attach to the stem by way of long petioles, and on the stem at either side of the petiole are small leafy bracts (stipules). Middle leaves are divided once into coarsely-toothed pointed lobes. Upper leaves are usually unlobed with smooth edges and without petioles so they are attached directly to the stem.

• Flowers:

  Each flower is composed of many yellowish disk flowers clustered onto a flat head that is about 1/10 inch wide. The inconspicuous flower heads are borne on upright branches arising from leaf axils on the upper part of the stem. The erect stem terminates in several to many flowering branches. Branches are often leafy, especially in the lower part.

• Fruits and Seeds:

  The single-seeded fruit is brown, ridged, oblong with a narrow base, and tipped with tiny bristles. Seeds of plants growing in temperate climates are usually not viable.

Similar Species:

The appearance of mugwort is similar to that of chrysanthemum species (Chrysanthemum spp.), tansy (Tanacetum vulgare), dogfennel (Eupatorium capillifolium), and horseweed (Conyza canadensis) except mugwort has dissected leaves that are white-wooly underneath, relatively inconspicuous flowers, and a sage-like aroma. Mugwort can be distinguished from other Artemisia species that are naturalized or cultivated around Ohio by its leaves, which are smooth on top and so hairy on the bottom that they appear white-wooly. Also, it has twice-divided lower leaves with pointed lobes.

Biology:

Mugwort blooms from July to September. Few germinable seeds are produced by plants growing in temperate regions in North America, so rhizomes are the main means by which mugwort reproduces. Cultivation and other practices that move soil tend to also move sections of rhizomes thus spreading and increasing the number of mugwort plants. The plant tolerates mowing. Therefore, it is relatively difficult to control this weed using only cultivation or mowing.

Toxicity:

Mugwort is said to cause dermatitis resulting from contact with skin or from drinking tea made from the weed.

Facts and Folklore:

• The common name 'mugwort' likely comes from the use of the plant to flavor beer.

• Many superstitions surround this plant; it was believed to provide protection from fatigue, sunstroke, wild animals, and evil spirits.