Mesclun is a mix of young, tender salad greens traditionally combining lettuces like arugula and radicchio with other greens such as spinach, chard, and mustard greens. It originated in Provence, in southern France, where the name comes from the Provencal Occitan word for "mixture" (related to the verb mesclar, "to mix").
Mesclun is typically dressed simply with a light vinaigrette to let the greens' flavors come through; in Italian cooking a similar mix underlies insalata mista. Its flavor ranges from arugula's peppery bite to spinach's mild sweetness, and it pairs well with grilled fish, poached eggs, roasted vegetables, nuts, and cheese.
Choose mesclun that is vibrant and crisp with no wilting, and use it within a few days; store it wrapped loosely in a damp paper towel in the refrigerator.