Ralph Waldo Emerson observed that a weed is a plant whose virtues have not yet been discovered. Yes, there are many plants that are found growing out of place that can be useful, including some that are edible. Conversely, there are many plants that have irritant or poisonous properties that ought to be avoided. It would be best to consult with references on weeds, native plants, or wildflowers that are specific to your location, and your local county Cooperative Extension agent can suggest such lists, books, or groups.

Err on the side of caution before consuming plants that may produce unwanted consequences. In addition, given that they are "weeds," make sure they have not been treated with pesticides before you start picking and chewing! This is more of a concern if you are foraging near public roads or railways.

Here are some references to look for in your local library:
* Stalking the Wild Asparagus (Euell Gibbons)
* Handbook of Edible Wild Plants and Weeds (Fern J. Ritchie)
* The Neighborhood Forager: A Guide for the Wild Food Gourmet (Robert K. Henderson)
* Edible Wild Plants: A North American Field Guide (Thomas S. Elias)
* The Encyclopedia of Edible Plants of North America (Francois Couplan)
* A Field Guide to Edible Wild Plants: Eastern and Central North America (Lee Allen Peterson)
* The Foraging Gourmet (Katie Letcher Lyle)
* Stalking the Healthful Herbs (Euell Gibbons)