Prostrate Knotweed

Prostrate Knotweed

Polygonum aviculare

This plant is real hard to find.  Just go outside and look in your driveway; it's probably there.  Some of the creeping spurges look like this too.  They're probably both in your driveway, unless you really keep your driveway clean.

To make it interesting, this species is known by a plethora of common names; Birdgrass, Doorweed, Waygrass, Knotgrass, Matgrass, Wireweed, Hogweed, Pinkweed, and Stonegrass are all names encountered via a web search of Polygonum aviculare.  I guess they couldn't figure out what to call it.  Just throw them all at it and see what sticks.