Horehound

Common Name(s)

Horehound

White horehound

Scientific Name

Marrubium vulgare

Family

Mint family (Lamiaceae)

Reasons for concern

This plant forms large, dense monocultures, which have a very negative impact on native vegetation, wildlife, and pollinators. Its dense root system makes it very difficult to eradicate.

Classification

Non-native

Botanical description

Can be upright like small shrub, or creeping. Entire plant has pungent/aromatic odor.

Leaves

Oval to circular. Opposite on stem. Grayish-green. Toothed (jagged) edges, located below flower whorl. Lower surface covered with white woolly hairs. Upper surface wrinkled or puckered. About 1 ½ inches long.

Stem(s)

Up to 3 feet tall. Usually erect, 4-sided, with a somewhat woolly base.

Flowers

Tiny to ¼ inch long, white, growing in dense round clusters where leaf meets stem. Tubular. Blooms April through September.

Seeds

Each flower produces 4 dark brown nutlets, each containing one seed.

Roots

Taproot, branched, woody, with numerous fibrous lateral roots.

Native to

Europe

Where it grows

Desert, uplands, mountain, riparian. Along roadsides. Disturbed places. Elevation 2,000 to 8,000 feet.

Lifecycle

Perennial

Reproduction

From seeds and spreading roots

Weedy Characteristics

Can form dense monoculture stands over large areas, reducing native plant diversity. Seeds can remain viable up to 5 years.

Control Strategies

Do not let them go to seed. Hand pull or dig out seedlings. Dig out more mature plants with the roots, but be careful not to disturb the soil too much. Step down any loose dirt to prevent seeds from finding a welcome environment to germinate. The roots make it very hard to eradicate. Repeatedly monitor previous infestations for new growth. You may need to consult a professional. Plant desirable native species to outcompete invasives.

Gallery

References

White horehound a weed report from the book Weed Control in Natural Areas in the Western United States , 2013, DiTomaso, J.M., G.B. Kyser et al. Weed Research and Information Center, University of California
Marrubium vulgare Texas invasive plant and pest council

View Printable PDF