 Within the genus there is considerable variation in the pappus, a structure that has traditionally been considered a key to defining genera in Asteraceae, and this led to earlier confusion in defining the genus.Most of the species of the genus were originally described as members of "Helianthus", based on having a pappus of two caducous awns.When it was recognized that they were not part of the exclusively North American "Helianthus", they were transferred to a genus called "Helianthopsis".