Every year about this time I get a few calls and samples sent in the mail (digital photo or fresh sample) asking what the name of this purple flowering plant. Many suspect that it is a member of the Phlox Family. That is not a bad guess, but it is incorrect. The purple flower I am referring to is called Damesrocket, Hesperis matronalis.

The key in distinguishing whether this plant is a member of the Phlox family or Damesrocket, is in the number of flower petals. Damesrocket will have four petals whereas Phlox flowers will have five petals. You will find Wild Blue Phlox, Phlox divaricata, and Damesrocket both growing along roadsides and in open areas. Damesrocket will grow to 1.5 to 3.5 feet in height, display multiple flowers on terminal branches, stems are erect branching near the top that are pubescent (short hairs). Leaves of Damesrocket are alternate, lance-shaped and the leaf margins may have teeth. Upper and lower surface of leaves are mostly pubescent. 

Ground-foraging birds eat seeds from Damesrocket. Although Damesrocket is not a serious weed for row crop production in Minnesota, it is an alternate host for beet mosaic, cauliflower mosaic, radish mosaic, squash mosaic, and turnip mosaic viruses. The purple-flowering plant flowers from May until August, can produce 20,000 seeds, and is most fragrant in the evening. It is quite common to find this plant growing in large patches.