This image is clicked on a random highway a few years back where this entire patch of land had weed plants growing wild like grass. You could just pluck it, crush it, roll it and smoke it. Some random high flyer would have thrown seeds here after a joint and voila we have an area filled with them.
The things you get to see sometimes can really astound you! Always keep your eyes open, as you never know what you might find at the very next turn.