Mystery flower identified

On my bike ride on August 18, I came across a small but pretty little flower growing along the trail above the Hildebrand lock & dam. Until today, it was labeled in my files as "tiny flower."
Today, thanks to the help of Donna Ford-Werntz, herbarium curator at WVU, we now have a name.

Ladies and gentlemen, meet the Willowleaf lettuce (Lactuca saligna).
Unfortunately -- I say this without sincerity -- this is a non-native species, originally from Eurasia.