Canada Thistle (Cirsium arvense)
It is a herbaceous perennial plant growing 30–100 cm, forming extensive clonal colonies from an underground root system that sends up numerous erect stems each spring. Contrary to what the name suggests, its origin is not Canadian.
Structure: Tall; can grow to 5′
Life Cycle: Perennial
What To Look For: Rather tall cluster of extremely spiky leaves first year; typical purplish thistle flower in second year, usually growing in clusters
Growth Period: June through September