Polygonum fowleri

About

Polygonum fowleri, commonly called Fowler's knotweed or Hudsonian knotweed, is a plant species native to the seashores of the northern part of North America. It has been reported from every Canadian province and territory except Alberta and Saskatchewan, as well as from Maine, Alaska, Washington, Oregon, California, and Saint Pierre and Miquelon. It is usually found in gravelly locations along the seacoast.

Summary from Wikipedia