A native of Europe, the bull thistle can now be found growing along roadsides all across the U.S., as well as in deserts, pastures and forests. It's easy to identify because of its very rough appearance, pain-inducing spines and purple flower head. The edible part is the young stalk. Scrape away the outer skin and spines, then eat the inner core as you would celery. Late in the season the stalks become too woody to eat.