Tall thistle (Cirsium altissimum) is a robust native plant. It can be 4′ to 10′ tall but in Minnesota it is usually no more than 7′ in height. It is found in prairies, open woodlands, roadsides, and disturbed sites. It has a patchy distribution in the lower two-thirds of Minnesota and is never common. It is absent from the far north and the Arrowhead region.
Tall thistle will easily pass the Native Thistle Test. Grasp the stem near the base of any native thistle loosely in your fist, then slide your fist upwards to just below the inflorescence. If the plant is a native thistle, you will not get a single prickle – it will be “ouchless”. If the thistle is thought to be an exotic (non-native) species, this test is not recommended.
Tall thistle looks similar to other native thistles. It can be distinguished by the stem that is green and not spiny; and the leaves that are white on the underside and are either unlobed or shallowly lobed.