Here in the Metro Denver area, garlic chives, garlic, and walking onions will self propagate and have except for when my hubby decides that he hates wild plants growing where he didn't establish them... so he digs them all up. I am slowly training him that this is a high desert and if something wants to grow in our yard and is edible, he should leave it alone!
I also have sorrel reseeding its self and slowly spreading around the front yard and strangely enough we are horrible at getting every little Peruvian purple potato out of the ground so they have been coming up every year for the last 5 years (I actually only purchased one start and now they are in every bed - I didn't even know that potatoes had seeds and could be spread probably by birds or squirrels). It actually makes it hard to do crop rotation and that sort of thing; but hey if they are growing well, who cares about that? Lastly, it looks like Orach is the salad and cooking green (well with red as well) that will grow here on its own... I didn't plant any this year but apparently something seeded itself from last year so I got about a dozen or so freebee plants that took off. We were harvesting quarts of greens/reds every day or two, so I ended up having to take a bunch to the food bank - 11 lbs one day even.
So I totally agree about the 3-4 plants per region/zone/area...
