Oh, I'm very aware of that... ;-) .. but those ones are kept under control by myself, and to a smaller extent my immediate neighbors (for excapees from my yard) via manual extraction. The window between sprouting and producing seeds is months, so they aren't hard to control within modest backyards - and I'm pretty far away from any rivers. The posting by Ken above just made we wonder whether I had missed a "loophole" (birds), but I don't think so.

Might be an Equisetum species, Horsetail or Scouring Rush. WW Here is a link that might be useful: Image search for Equisetum

Thank's to both of you! I am pretty sure the Lavatera at the link you recommended is right.

Not sure. Maybe Ohio Spiderwort?