I have NO idea what happened, or if it's just rain, but we have literally zillions of the same kind of thing sprouting everywhere. It is particularly bad in the new beds where we ripped out some lawn, but we also have a lot that showed up in our containers, all over the lawn, etc.. I've got it a bit under control, but only after having pulled a TON of them. They are even sprouting through the mulch, around and between the main stems of our 'real' plants like the impatiens. Does anyone know what this stuff is (the serrated leafy thing in the foreground)? I believe it grows into a larger plant with the same kind of leaf. Appreciate any help since I'd like to prevent it from happening in future! I don't remember it happening last year.