Veronica peregrina

from WordNet (r) 3.0 (2006)

Veronica peregrina
    n 1: North American annual with small white flowers widely
         naturalized as a weed in South America and Europe [syn:
         {purslane speedwell}, {Veronica peregrina}]

from The Collaborative International Dictionary of English v.0.48

Neckweed \Neck"weed`\, n. (Bot.)
   (a) An American annual weed ({veronica peregrina}), with
       small white flowers and a roundish pod.
   (b) The hemp; -- so called as furnishing ropes for hanging
       criminals. --Dr. Prior.
       [1913 Webster]