Petrorhagia

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

Petrorhagia proliferaCHILDING PINK 
Petrorhagia saxifragaPINK 

Citation:

MICHIGAN FLORA ONLINE. A. A. Reznicek, E. G. Voss, & B. S. Walters. February 2011. University of Michigan. Web. April 28, 2017. http://michiganflora.net/genus.aspx?id=Petrorhagia.