Prostrate knotweed is a low-growing summer annual found in lawns throughout the United States. It grows well in heavily trafficked areas. A long taproot allows it to survive hot, dry periods. The branching stems form a dense mat that can be 2 to 3 feet wide.
You will often find knotweed in sports fields, paths, driveways, along roadsides...it grows and thrives in hard, compacted soils.
It can be confused with Spotted Spurge. However, the spurges ooze a milky sap when their stems are cut.