This week’s weed comes to you courtesy of Ryan Goodman (@AR_ranchhand, blog).  While out checking cows one afternoon Ryan came across purple mint in the pasture and sent me these photos of the weed.  Purple mint (Perilla fructescens), also known as Perilla mint or Beef-steak plant, is an annual herb of the genus Perilla of the mint family, Lamiaceae.

This herb is erect standing 1/2 to 2 feet in height with distinctive green or purplish-green leaves with toothed margins. These plants emit a distinctive minty odor, especially when mature. Perilla mint is primarily a weed of pastures, hay fields, fencerows, and roadsides. This plant is extremely toxic to all kinds of cattle, sheep, and horses and causes more cattle deaths in Tennessee than any other toxic plant.  To read more about the toxic effects of Purple mint on cattle and how to prevent toxicity check out this extension publication from the University of Tennessee.

Leaves are arranged oppositely along the stem, green in color, most often with a distinct purple tinge.  Individual leaves are oval-shaped, approximately 2 to 5 inches long, 1 1/2 to 4 inches wide.  Leaves occur on petioles, have distinctly toothed margins and emit a minty odor when crushed.

Many flowers occur in terminal clusters giving the mature plant a ‘bottle-brush’ appearance. Individual flowers are small, white to whitish-purple in color, hairy, with an upper lip that is 3-toothed and a lower lip that is 2-toothed.

The distinctive minty odor and oval, green to purple leaves with toothed margins are all characteristics that help in the identification of perilla mint. Hophornbeam copperleaf (Acalypha ostryifolia) has similar leaves and growth habit, but does not have the characteristic minty odor and greenish purple leaves like those of perilla mint.

Source: Virginia Tech Weed ID Guide