| | 1. Midvein of phyllary brown, resin-filled |
| |
| | 2. Heads disciform (pistillate flowers liguleless) |
| C. bilbaoana |
| | 2' Heads radiate; ligules present (generally < 1 mm) |
| C. canadensis |
| | 1' Midvein of phyllary green to purple, not resin-filled |
| |
| | 3. Leaves clasping, regularly dentate or spreading-lobed; herbage densely glandular; pistillate flower styles long-exserted |
| C. coulteri |
| | 3' Leaves not clasping, generally entire (or lower irregularly serrate to ascending-lobed); herbage gray-hairy, not or barely glandular; pistillate flower styles ± = corollas |
| |
| | 4. Central stem generally overtopped by lateral branches; pressed heads generally ± 1 cm wide; dry, reflexed phyllaries whitish or dull brown inside |
| C. bonariensis |
| | 4' Central stem > lateral branches (unless plant damaged); pressed heads generally < 1 cm wide; dry, reflexed phyllaries reddish brown inside |
| C. floribunda
|