1. Phyllaries (outer) 3–5 (–6) mm wide below the middle; heads ca. 4–9 cm in diameter, nodding at maturity and solitary at the ends of branches.
1. Phyllaries less than 2 mm wide; heads less than 4 cm in diameter, erect, solitary or clustered on branches.
2. Lower surface of leaves glabrate except for long, curled, septate hairs along veins.
2. Lower surface of leaves sparsely to densely tomentose with fine, non-septate hairs and often with curled, septate hairs along veins as well.
All species found in Carduus
MICHIGAN FLORA ONLINE. A. A. Reznicek, E. G. Voss, & B. S. Walters. February 2011. University of Michigan. Web. March 23, 2019. https://www.michiganflora.net/genus.aspx?id=Carduus.