Tall blue lettuce (Lactuca biennis), tall wild lettuce (L. canadensis), and prickly lettuce (L. serriola), are the most common types of wild lettuce. All have milky sap. The prickly lettuce is often called compass plant because the leaves tend to align themselves in a north-south position.
Photo by Dr. John Meade, weed scientist emeritus
Rutgers NJAES Cooperative Extension