Persicaria amphibia (L. ) Gray (Polygonum amphibium L.)

Abstract

A versatile rhizomatous perennial, one of the rather few truly amphibious plants (Rodwell 1995), with aquatic and terrestrial forms so different that the uninitiated may think that they are different species (Lousley & Kent 1981). Aquatic form. Pale, branching rhizomes < 0.2 m deep in underwater substrate (Best & Dassen 1987), and < 2 m under water (Spence in Veg. Scot.), carry perennating buds that produce pliable, sparsely branching stems with vestigial leaves and rings of adventitious roots; interodes 5-40 cm (Arber 1920). Stems branch < 10 cm underwater, and bear alternate floating leaves: blades pliant, waxy, smooth, 4-10 cm long, 2-4 cm wide, lanceolate/narrow-ovate, margin entire or minutely toothed; petioles 2-8 cm, flexible. Ochreae entire, membranous, semitranslucent, secreting mucilage around axillary bud. In early summer, shoots surface with 1-3 aerial leaves and inflorescences. Peduncle glabrous or sparsely hairy + stalked glands; otherwise aquatic form entirely glabrous. Terrestrialform. + glabrous, glandular-hairy, finely to coarsely pubescent or appressed-hispid. Rhizomes < 50 cm deep produce procumbent/erect stems, 0.4-1 (-2) m, branching below, little-branching above; internodes 1-4 cm, nodes (+ root-precursors) swollen. Ochreae entire, green, hairs (if present) may exceed margin. Petioles + rigid, 0.5-1.5 cm, blades 4-14 cm long, 1-3 cm wide, more opaque, coarse and inflexible than in aquatic form, lanceolate, margin fine-toothed, immature/early leaves often with dark chevron-shaped blotches.