What is this shrubby plant?
I have this plant in my front yard (in the foothills of Reno, NV), growing up through the landscape rocks. I can't tell if it's been planted by the previous owners (who also intentionally planted holly bushes to block access to the gates to the back yard, but that's another issue) or if it sprung up during the year and a half the house was vacant. It's very fast-growing and according to my neighbors has tiny pink or white flowers in the summer.
Close-up of stem/leaves: