Nodding Thistle,  Carduus nutans
Asteraceae or Sunflower Family

Flower head Tall prickly plant to 6 feet tall. Leaves lobed and toothed with spines on ends of teeth. Stems also spiny. Flowerheads nodding, containing many purple disk flowers in a pom-pom, above spiny bracts, on a naked flowerstalk.

Attractive but unfriendly alien weed of roadsides and waste places. In Wildwood found around Outdoor classroom and to be expected occassionally in open disturbed places.

Bull thistle is a similarly prickly alien weed of similar habitat, but its flowers do not nod, and the flowerstalk is also prickly.