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Bidwell knotweed, Bidwell's knotweed

seabeach knotweed, seaside knotweed

Habit Herbs. Plants silvery, homophyllous.
Stems

erect, green, simple or divaricately branched, ± wiry, 2–20 cm, minutely papillose-scabridulous.

prostrate to ascending, branched from base, not wiry, 20–70 cm.

Leaves

crowded at branch tips, not articulated to ocreae, basal leaves caducous or persistent, distal leaves abruptly reduced to bracts;

ocrea 8–13 mm, papillose-scabridulous, proximal part cylindric, distal part overlapping and obscuring leaves and flowers, silvery, entire or shallowly dentate;

petiole absent;

blade 3-veined, without pleats, linear, 5–15(–20) × 0.5–1.5(–2) mm, margins revolute, papillose-denticulate, apex spine-tipped.

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;

cymes in distal axils, 1-flowered.

axillary;

cymes uniformly distributed, 1–3-flowered.

Pedicels

absent.

enclosed in ocreae, 3–5 mm.

Flowers

closed;

perianth 2–3 mm;

tube 10–18% of perianth length;

tepals overlapping, pink with pink or white margins, petaloid, elliptic, navicular, apex acute to acuminate;

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 at maturity, light brown to brown, ovate-elliptic, 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.

Polygonum bidwelliae

Polygonum glaucum

Phenology Flowering May–Jun. Flowering Jul–Nov.
Habitat Thin volcanic soils, chaparral, montane woodland valleys, grasslands Coastal beaches, sand dunes, margins of salt ponds
Elevation 60-1200 m (200-3900 ft) 0-10 m (0-0 ft)
Distribution
from FNA
CA
[WildflowerSearch map]
[BONAP county map]
from FNA
CT; DC; DE; FL; GA; MA; MD; NC; NJ; NY; RI; SC; VA
[BONAP county map]
Discussion

Polygonum bidwelliae occurs in the Cascade Range and northeastern Sacramento Valley in Butte, Shasta, and Tehama counties.

(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. 565. FNA vol. 5, p. 553.
Parent taxa Polygonaceae > subfam. Polygonoideae > Polygonum > sect. Duravia Polygonaceae > subfam. Polygonoideae > Polygonum > sect. Polygonum
Sibling taxa
P. achoreum, P. argyrocoleon, P. austiniae, P. aviculare, P. bolanderi, P. californicum, P. cascadense, P. douglasii, P. engelmannii, P. erectum, P. fowleri, P. glaucum, P. heterosepalum, P. hickmanii, P. humifusum, P. majus, P. marinense, P. minimum, P. nuttallii, P. oxyspermum, P. paronychia, P. parryi, P. patulum, P. plebeium, P. polygaloides, P. ramosissimum, P. sawatchense, P. shastense, P. spergulariiforme, P. striatulum, P. tenue, P. utahense
P. achoreum, P. argyrocoleon, P. austiniae, P. aviculare, P. bidwelliae, P. bolanderi, P. californicum, P. cascadense, P. douglasii, P. engelmannii, P. erectum, P. fowleri, P. heterosepalum, P. hickmanii, P. humifusum, P. majus, P. marinense, P. minimum, P. nuttallii, P. oxyspermum, P. paronychia, P. parryi, P. patulum, P. plebeium, P. polygaloides, P. ramosissimum, P. sawatchense, P. shastense, P. spergulariiforme, P. striatulum, P. tenue, P. utahense
Name authority S. Watson: Proc. Amer. Acad. Arts 14: 294. (1879) Nuttall: Gen. N. Amer. Pl. 1: 254. (1818)
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