Would you like a plant that grows anywhere? How about oxalis, also called wood sorrel? This is some growing in a bucket of rocks that I have on my patio. I haven't figured out what to do with the rocks, but in the meantime, the oxalis has apparently decided that this would be good place to "give it a go".
I've noticed that oxalis picks the poorest soils around my garden to try to grow, places like up by the house where it is too dry or sandy or infertile for any other plants. In fact, I've decided that where I find oxalis, I probably have a soil fertility problem!