Halberd-leaf tearthumb, renouée à feuilles d'arum

Polygonum arifolium Linnaeus, Sp. Pl. 1: 364. 1753; P. arifolium var. lentiforme Fernald & Griscom; P. arifolium var. pubescens (R. Keller) Fernald; P. sagittatum Linnaeus var. pubescens R. Keller; Tracaulon arifolium (Linnaeus) Rafinesque; Truellum arifolium (Linnaeus) Soják

Plants annual, 2-15 dm; roots also often arising from proximal nodes. Stems scandent, ribbed, glabrous; prickles 0.5-1 mm. Leaves: ocrea tan or brownish, cylindric, 8-15 mm, chartaceous, base inflated or not, with prickles, margins oblique, ciliate with bristles 0.5-2.5 mm, surface glabrous or appressed- to spreading-pubescent; petiole 1-7 cm; blade broadly hastate to hastate-cordate or triangular, (2-)6.5-13(-18) × (1-)6-11(-16) cm, base truncate to truncate-cordate, margins broadly hastate with lobes divergent, ciliate, sometimes also retrorsely prickly, apex acuminate, faces appressed-pubescent or, rarely, glabrous adaxially, stellate-pubescent or, rarely, glabrous abaxially, major veins often bearing prickles. Inflorescences capitate or paniclelike, uninterrupted, 5-12 × 3-8 mm; peduncle 10-80 mm, retrorsely prickly proximally, stellate-pubescent and stipitate-glandular distally, glands red or pink; ocreolae usually overlapping, sometimes not overlapping proximally, margins eciliate or ciliate with bristles to 0.5 mm. Pedicels mostly ascending, 2-3 mm. Flowers 2-4 per ocreate fascicle; perianth pink or red, often whitish green proximally, glabrous, accrescent, not becoming blue and fleshy in fruit; tepals 4, connate 3- 2 their length, broadly elliptic, 5-6 mm, apex acute to obtuse; stamens (6-)8, filaments distinct, free; anthers pink, elliptic; styles 2, distinct. Achenes included, dark brown to black, biconvex, 3.5-6 × 3-4 mm, shiny, smooth.

Flowering Jul-Oct. Shaded swamps, ponds, tidal marshes along rivers, wet ravines in forests; 0-600 m; N.B., N.S., Ont., P.E.I., Que.; Conn., Del., D.C., Ga., Ill., Ind., Ky., La., Maine, Md., Mass., Mich., Minn., Mo., N.H., N.J., N.Y., N.C., Ohio, Pa., R.I., S.C., Tenn., Vt., Va., Wash., W.Va., Wis.