Asteraceae, the Aster family, are mostly soft-stemmed herbs, though some species have woody stems and become shrub-like. This family is also known as the composites, since plants produce compound flowerheads, usually with a center of small tubular flowers known as disc florets surrounded by a ring of broader, flat flowers, the ray florets. Some species have only discs, and some only rays, while others, such as the common dandelion, have florets that are intermediate in appearance.

Asteraceae is the second biggest plant family an the world, but the largest in the US, with around 477 genera and 2,862 species. They are found in every part of the US, but especially in woodland, grassland and sagebrush. Many species look similar, and assignment can often be difficult; one component useful for identification are the phyllaries, below the flowerhead; their shape, coloration, hairiness and glandularity are often quite distinctive.