They were separated on the basis of morphological differences, such as the arrangement of the flower heads in the inflorescence and the glands on the leaves, and of DNA data.

[5] They are native to North America, but certain species are introduced in Europe and Asia.

[7] These species are quite variable in appearance, the variation often influenced by environmental conditions.

The flower heads are solitary or borne in a dense or spreading array.

The fruit is a rough-textured cypsela tipped with a pappus of white bristles.