1. Phyllaries (outer) 3โ5 (โ6) mm wide below the middle; heads ca. 4โ9 cm in diameter, nodding at maturity and solitary at the ends of branches.
C. nutans
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.
C. acanthoides
2. Lower surface of leaves sparsely to densely tomentose with fine, non-septate hairs and often with curled, septate hairs along veins as well.
C. crispus
All species found in Carduus
Citation:
MICHIGAN FLORA ONLINE. A. A. Reznicek, E. G. Voss, & B. S. Walters. February 2011. University of Michigan. Web. January 26, 2021. https://michiganflora.net/genus.aspx?id=Carduus.