Hesperis matronalis, right there on the trail

On the Billy Goat B Trail near the Marsden Tract, about ten days ago, there was a great stand of tall plants blooming in various shades of purple. In past years other hikers have asked me if I knew what the plants are. They’re so beautiful and eye-catching!

four-petaled flowers of Hesperis matronalis

And, guess what? As is too often the case with showy flowers, this species is an alien invasive. Its common name is dame’s rocket; the botanical name is Hesperis matronalis. The four-petaled flowers are typical of plants in the mustard family (Brassicaceae).

Phlox divaricata

Beginning wildflower enthusiasts sometimes mistake dame’s rocket for our native wild blue phlox (Phlox divaricata), which has flowers in a similar range of colors. However, wild blue phlox is usually done blooming by the time dame’s rocket is starting.

alternate leaves with serrated margins on Hesperis matronalis

Also, the phlox is a shorter plant and has opposite leaves with entire margins, whereas dame’s rocket has alternate leaves with serrated margins.

range of colors in a stand of Hesperis matronalis

Dame’s rocket ranges through almost all of Canada and the US, except for the southernmost tier of states. It’s listed in Colorado as a noxious weed; is invasive, banned in Connecticut; and is prohibited in Massachusetts. The Missouri Botanical Garden website says, in bold red letters:

This plant is listed as an exotic invasive species to Missouri and the Midwest by the Midwest Invasive Plant Network. The species should not be planted in the Midwest.

It shouldn’t be planted in Maryland, either. It self-seeds like crazy. Come to think of it, wild blue phlox would make a wonderful substitute in the home garden. Unless you have rabbits. The rabbits destroyed mine within two days of planting last spring.

a single Hesperis matronalis on the other side of the trail

The generic name Hesperis is from the Greek word for evening, in reference to the pleasant fragrance the plants give at dusk.