I noticed this weed a few weeks ago and am not familiar with it. It is starting to spread across my lawn and despite my normal efforts to kill the weed it still persists. I tried to scour the net and see if I could identify it, but the closest I could come up with was a weed not indigenous to Houston or even Texas. Not especially evident in these pics is a tiny flower at the center, what looks to be a 5-petal flower. It can be seen in the broad picture, but the one I picked does not have it. Any help at all would be most appreciated. Thanks!

Chris