Fowler's Knotweed

Plants green, sometimes purple tinged, homophyllous or hetero-phyllous, sometimes subsucculent. Stems prostrate to ascending, sometimes zigzagged, branched from base, not wiry, 5-50 cm. Leaves: ocrea 2.5-12 mm, proximal part funnelform, distal part soon disintegrating, nearly completely deciduous or fibers persistent; petiole 2-7 mm; blade light green, sometimes purple tinged, elliptic to elliptic-obovate or obovate, 8-30(-50) × 4-15(-25) mm, margins flat, apex acute to obtuse; middle stem leaves 1.1-2.1(-3.4) times as long as adjacent branch leaves, distal leaves overtopping flowers. Inflorescences axillary; cymes uniformly distributed, 1-7(-10)-flowered. Pedicels enclosed in or sometimes exserted from ocreae, 1-2.5 mm. Flowers closed; perianth (2.2-)2.5-4.5 mm; tube 23-38% of perianth length; tepals initially overlapping, pushed apart as achene develops, green, margins white to pink, petaloid, not keeled, oblong, cucullate; midveins branched, sometimes not visible; stamens 6-8. Achenes exserted from perianth, brown to dark brown, broadly ovate to ovate-lanceolate, (2-)3-gonous, (1.8-)2-3.7(-4.5) mm, faces subequal or unequal, flat to concave, apex beaked, edges strongly concave, shiny to dull, roughened, rarely obscurely tubercled; late-season achenes common, 4-6 mm.

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 St. Pierre & Miquelon. It is usually found in gravelly locations along the seacoast.

Polygonum fowleri is a prostrate to ascending herb, often with zigzagged stems. Inflorescences are in the axils of the leaves, each with up to 10 white or pink flowers.

Subspecies

Two subspecies are recognized, treated by some botanists as distinct species:

Polygonum fowleri subsp. fowleri – shores of Atlantic, Pacific, and Arctic Oceans Polygonum fowleri subsp. hudsonianum (S. J. Wolf & McNeill) Costea & Tardif (= P. hudsonianum (S. J. Wolf & McNeill) H. R. Hinds) – shores of Hudson Bay, the Canadian Arctic Islands, and the Atlantic coast of Labrador, Newfoundland, and Nova Scotia