This thistle is also sometimes called Nodding Thistle. The red-purple flower of Musk Thistle is about two inches in diameter, which is larger than other biennial thistles (i.e., Bull and Tall) and perennial thistles, such as Canada Thistle. The drooping or nodding flower head is surrounded by broad, spiny-tipped bracts which are quite attractive. The tall plant in my photo was already past its prime, which is why I took it from behind.