Sometimes edibles in a city are handy. I have made a tea out of willow bark for a headache that my lady friend had. we were at a park in the middle of town. She didn't want to leave and I didn't want her to be in pain. She was surprised when it worked. Granted if the SHTF wild edibles would be a low priority in a major city, but if its TEOTWAWKI then it could be life saving. I would get out of the city quickly, but Reasons beyond my control could prevent that. I am thinking of the movie Legend. Then it could save your bacon.

What grows in a city can also grow outside a city. So knowing the wild, or introduced, edibles in your area is a good thing, assuming that you would like to survive any possibility.