Polygonum nuttallii |
Polygonum glaucum |
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Nuttall's knotweed |
seabeach knotweed, seaside knotweed |
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Habit | Herbs. | Plants silvery, homophyllous. |
Stems | spreading to erect, sometimes zigzagged, purplish, simple or branched, wiry, (5–)10–35 cm, papillose-scabridulous. |
prostrate to ascending, branched from base, not wiry, 20–70 cm. |
Leaves | evenly distributed or crowded at branch tips, articulated to ocreae, basal leaves persistent, distal leaves gradually reduced to bracts; ocrea 3–4 mm, papillose-scabridulous, proximal part funnelform, distal part finely lacerate; petiole 0.1–2 mm; blade 1-veined, not pleated, linear to narrowly oblong-elliptic, 8–30 × 1–4(–7) mm, margins narrowly revolute, never touching along midrib, smooth, apex acute, mucronate, ± glaucous adaxially. |
ocrea persistent, 7–15 mm, proximal part cylindric, pruinose, distal parts silvery, margins overlapping, entire or lacerate; petiole 0.5–3 mm; blade bluish green, lanceolate, 10–30 × 2–8 mm, coriaceous, margins revolute, apex obtuse or acute, rugulose when fresh, markedly rugulose when dried, glaucous; middle stem leaves slightly larger than adjacent branch leaves, distal leaves overtopping flowers they subtend. |
Inflorescences | axillary and terminal, spikelike, dense; cymes mostly congested toward tips of branches, 2–3-flowered. |
axillary; cymes uniformly distributed, 1–3-flowered. |
Pedicels | enclosed in ocreae, erect to spreading, 2–3 mm. |
enclosed in ocreae, 3–5 mm. |
Flowers | semi-open or closed; perianth 1.8–2.4 mm; tube 25–33% of perianth length; tepals overlapping, greenish, white, or pink with pink margins, petaloid, oblong, cucullate, navicular in distal 1/4, apex rounded; midveins unbranched; stamens 8. |
semi-open; perianth (2–)3–4 mm; tube 12–26% of perianth length; tepals ± recurved, overlapping, white, margins white or pink, petaloid, not keeled, oblong-obovate to spatulate, not cucullate; midvein usually unbranched; stamens 8. |
Achenes | enclosed in perianth, black, elliptic to ovate, 1.8–2.3 mm, faces subequal, shiny, smooth. |
exserted from perianth, reddish brown to dark brown, ovate, 3-gonous, 2.5–3(–4) mm, faces subequal, apex not beaked, edges straight, shiny, smooth; late-season achenes common, 3–5 mm. |
2n | = 40. |
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Polygonum nuttallii |
Polygonum glaucum |
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Phenology | Flowering May–Oct. | Flowering Jul–Nov. |
Habitat | Dry prairies, open knolls in lower mountains, open sites in lowland and montane zones, sandy soil | Coastal beaches, sand dunes, margins of salt ponds |
Elevation | 800-1100 m (2600-3600 ft) | 0-10 m (0-0 ft) |
Distribution |
OR; WA; BC
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CT; DC; DE; FL; GA; MA; MD; NC; NJ; NY; RI; SC; VA |
Discussion | C. L. Hitchcock (1964) suggested that Polygonum nuttallii is but a small-flowered form of P. spergulariiforme. Although morphologically similar, P. nuttallii differs from P. spergulariiforme in some respects, including its wiry, purplish stems, short and funnelform ocreae, adaxially glaucous leaves, longer bracts, shorter fruiting perianth, and achenes. (Discussion copyrighted by Flora of North America; reprinted with permission.) |
Polygonum glaucum is restricted to maritime beaches along the Atlantic coast from Massachusetts south to Georgia. Over most of its range it is rare and declining; populations on coastal islands of Massachusetts and along the shore of Long Island appear to be secure. Seabeach knotweed appears to be related to P. oxyspermum. (Discussion copyrighted by Flora of North America; reprinted with permission.) |
Source | FNA vol. 5, p. 570. | FNA vol. 5, p. 553. |
Parent taxa | Polygonaceae > subfam. Polygonoideae > Polygonum > sect. Duravia | Polygonaceae > subfam. Polygonoideae > Polygonum > sect. Polygonum |
Sibling taxa | ||
Synonyms | P. intermedium, P. douglasii subsp. nuttallii | |
Name authority | Small: Mongr. Amer. Sp. Polygonum, 132, plate 53. (1895) | Nuttall: Gen. N. Amer. Pl. 1: 254. (1818) |
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