Sticky Geranium in Yellowstone
The Sticky geranium or "Sticky cranesbill" (Geranium viscoissimum) has five pink-to-purple leaves in loose clusters with deeply-lobed, toothed leaves. It favors open forests and mountain sagebrush grasslands.
Similar plants include Richardson's geranium (Geranium richardsonii), with whiter petals and purple veins.
Photo taken on the Beaver Ponds trail, a little north of the Montana border, June 2009.