1. Flowers in a head, closely enveloped by large scarious-margined bracts; calyx (mostly hidden by bracts) ca. 9–12 mm long.
P. prolifera
1. Flowers solitary; calyx ca. 3–5 mm long (not hidden by bracts).
P. saxifraga
All species found in Petrorhagia
Citation:
MICHIGAN FLORA ONLINE. A. A. Reznicek, E. G. Voss, & B. S. Walters. February 2011. University of Michigan. Web. June 21, 2018. https://michiganflora.net/genus.aspx?id=Petrorhagia.