The Spotted Knapweed (Centaurea maculosa) is a pesky, biennial herb reproducing by seeds. Its erect stems with wiry branches are somewhat hairy and rough to the touch. The flower heads resemble thistle heads, but the flower heads of the Knapweed are surrounded by prickly black-tipped bracts (see photo). Lavender to white-colored flowers may resemble the well-known Cornflower or Bachelor's Button, but the Knapweed is far less showy and colorful.
This species was introduced and naturalized from Europe, and has spread throughout the northeastern part of the United States. Apparently, it continues to spread southward, especially in the Piedmont areas. Back in 1960 I found the Knapweed to be fairly rare and photographed the plant that was established along the Franklin Turnpike near Callands. Nowadays, it has abundantly spread to old fields and roadsides in dry, sterile, sandy soils. Spotted Knapweeds may reach a height of 3 feet (1 meter).