I have no clue ... the first time I ever saw them was Jan. 2011 at our old house, one popped up in the yard. Then in Jan 2013 one showed up here at our current home in a flower bed amid some rocks. Dec. 2014 one popped up in a container again and just a few days ago I noticed one sprouting in a container plant. I've read that some consider it a nuisance weed but I haven't found it to be spreading, invasive or a nuisance at all.
