Renouée à fleurs jaunes

Polygonum atlanticum (B. L. Robinson) E. P. Bicknell; P. exsertum Small; P. interior Brenckle; P. latum Small ex Rydberg; P. leptocarpum B. L. Robinson; P. stevensii Brenckle; P. triangulum E. P. Bicknell

Plants usually yellowish greenish when fresh or dried, hetero-phyllous. Stems 30-200 cm. Leaf blades light yellowish green, narrowly elliptic to lanceolate, rarely ovate, 35-70 × 7-18(-35) mm, apex acute to acuminate; stem leaves 2.1-3.5(-4.2) times as long as branch leaves; distal leaves usually 1-2 mm, not overtopping flowers, or 5-15 mm, surpassing flowers. Inflorescences axillary and terminal, spikelike; cymes crowded toward tips of branches, 2-5-flowered. Pedicels exserted from ocreae, 2.5-6 mm. Flowers: perianth (2.6-)3-4 mm; tepal margins greenish yellow or yellow, rarely white or pink; stamens 3-6(-8). Achenes enclosed in or exserted from perianth, (2.3-)2.5-3.5 mm, shiny or dull, smooth to roughened, sometimes uniformly or obscurely tubercled; late-season achenes 5-12 mm. 2n = 60.

Flowering Jul-Oct. Disturbed places, sandy shores or saline soils and shores; 0-1000 m; Alta., B.C., Man., N.B., N.W.T., N.S., Ont., P.E.I., Que., Sask.; Ariz., Ark., Calif., Colo., Conn., Del., Ga., Idaho, Ill., Ind., Iowa, Kans., Ky., La., Maine, Mass., Mich., Minn., Mo., Mont., Nebr., Nev., N.H., N.J., N.Mex., N.Y., N.C., N.Dak., Ohio, Okla., Pa., R.I., S.C., S.Dak., Tenn., Tex., Utah, Vt., Va., Wash., Wis., Wyo.

Subspecies ramosissimum is heterogeneous; some additional elements may deserve recognition. It is closely related to European Polygonum bellardii Allioni, which was collected in south Boston in 1785 (B. L. Robinson 1902). The latter species has semi-open flowers, petaloid tepals with white or pink margins, and eight stamens. A distinct form of P. ramosissimum growing in saline marshes from California has been mistakenly identified as P. patulum Bieberstein (M. Costea and F. J. Tardif 2003b). The morphology of late-season achenes and the branching patterns, which have been emphasized by some authors, appear to have little taxonomic value.