Tall Bellflower - Campanulastrum americanum

Campanulastrum americanum, or Tall Bellflower, is a self-sowing biennial wildflower native to southern Michigan and Wisconsin. Plant reaches 3 to 5 feet tall and flowers from July to October with a showy spike of blue-lavender flowers. It prefers partial sun to full shade, medium to dry soil and will grow in clay, loam or sand, but the preference is for dappled light and forest loam under deciduous trees. 
 
This flower is used by long-tongued bees such as bumblebees and leaf cutter bees, and is also a nectar and pollen resource for the specialist bee Megachile campanulae campanulae (per the Illinois Wildflowers website). It also attracts butterflies.