Prickly Lettuce / Lactuca serriola

This plant is the closest wild relative of cultivated lettuce (Lactuca sativa L.). Also called prickly lettuce, milk thistle, compass plant, and scarole. The flower heads are 11 to 13mm wide, are pale yellow, often tinged purple. The bracts are also often tinged purple. The leaves of this plant often point east and west, giving it the common name "Compass-plant". It is an introduced plant, from Europe. Photographed when a group of us visited the Beynon Ecological Preserve (Nature Conservancy of Canada), near Drumheller, in the Badlands of Alberta, on 3 August 2013.

en.wikipedia.org/wiki/Lactuca_serriola