As the common name suggests, this thistle can become quite tall. It resembles Cirsium discolor (Pasture Thistle) and other common thistles, except that its leaves are less pinnatifid and spiny. The native Pasture Thistle prefers habitats that are more dry and sunny, but it is also sometimes found in wooded habitats. An aggressive Eurasian species, Cirsium vulgare (Bull Thistle), also prefers habitats that are more dry and sunny; it is even more heavily armed with spines than the Pasture Thistle. Unlike the Tall Thistle and Pasture Thistle, the Bull Thistle has leaf undersides that are more green because they are less densely hairy. The leaf undersides of the preceding native thistles are bright white because they have dense mats of white-woolly hairs. All of these tall-growing thistles are in bloom at about the same time of year and their erect flowerheads are pink to purplish pink.