Common St. John's-wort (Hypericum perforatum) is a common perennial of fields, roadsides, and other open areas with disturbed soil. In June and July, the yellow flowers of this weedy species stand out (see Medicinal Weeds: Common St. John's-wort). During the white season, if not blanketed by feet of snow, the dried stalks of Common St. John's-wort can still be recognized.
Look for 2-3' tall, round-stemmed stalks with numerous, oppositely arranged, up-swept branches topped with 1/4" tall, reddish-brown, three-parted capsules containing many tiny seeds. (You might want to read that again, slowly.)