Polygonum glaucum, common names seabeach knotweed and seaside knotweed, is a North American species of plants in the buckwheat family. It grows on the Atlantic Coast of the United States, from Alabama to Massachusetts, including in salt-water inlets such as Chesapeake Bay and the Hudson River. Polygonum glaucum is a branching herb up to 70 cm (28 in) tall. It appears silvery of bluish-green because of wax covering the leaves and stem. Flowers are pink or white, produced in groups of 1-3. It grows on beaches, sand dunes, and the edges of coastal marshes.