What plant is this?

This is my second Spring in this house, and I'm seeing a bunch of seedlings (?) that I didn't see last year. The plant has 2 starter leaves that give way to a long,pointed leaf that is red on its underside. I'm eager to identify it, so I know whether or not to start weeding them. I'm trying to keep a collection of native plants in the yard, and this is one that I'm unsure of. Can anyone help me to ID it? Thanks...

 

looks like a Persicaria type of leaf (you hav'nt got japanese knot weed near have you?)

 

There is knot weed in the area, but I haven't seen any in/around my yard. I hope not, as I hear it is very difficult to get rid of.

 

These are one of the annual species.