These are the young and tender shoots of a type of wild thistle plant. These plants can be steamed or baked in gratins, and have a delicate, nutty flavor. It's quite uncommon and rare to see these in the market because they have a very short growing season, and most people simply don't know what to do with them; they were more common in ancient times when humans foraged for food.
Related: Found Food: Do You Forage for Food?
(Image: Kathryn Hill)