carpetweed

American Heritage® Dictionary of the English Language, Fourth Edition

1. n. A prostrate, mat-forming annual plant (Mollugo verticillata) widespread as a weed throughout North America and having whorled leaves and small, greenish-white flowers.

WordNet 3.0

1. n. annual prostrate mat-forming weed having whorled leaves and small greenish-white flowers; widespread throughout North America