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birdweed, common knotgrass, common knotweed, doorweed, dooryard knotweed, knotgrass, knotweed, lowgrass, pigweed, prostrate knotweed, renouée des oiseaux, yard knotweed

seabeach knotweed, seaside knotweed

Habit Plants green or bluish green, green after drying, sometimes whitish from powdery mildew, homophyllous or heterophyllous. Plants silvery, homophyllous.
Stems

prostrate to erect, branched, flexuous, 5–200 cm.

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

Leaves

ocrea 3–15 mm, proximal part cylindric or ± funnelform, distal part silvery, hyaline, soon disintegrating into persistent fibers or nearly completely deciduous;

petiole 0.3–9 mm;

blade green to gray-green, narrowly elliptic, lanceolate, elliptic, obovate, or spatulate, 6–50(–60) × 0.5–22 mm, margins flat, apex acute, obtuse, or rounded;

stem leaves 1–4 times as long as adjacent branch leaves;

distal leaves overtopping flowers.

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 uniformly distributed or aggregated at tips of stems and branches, 1–6(–8)-flowered.

axillary;

cymes uniformly distributed, 1–3-flowered.

Pedicels

enclosed in or exserted from ocreae, 1.5–5 mm.

enclosed in ocreae, 3–5 mm.

Flowers

closed or semi-open;

perianth 1.8–5.5 mm;

tube 20–57% of perianth length;

tepals overlapping or not, green or reddish brown with white, pink, or red margins, petaloid, not keeled, oblong to obovate, often cucullate in fruit;

midveins branched or unbranched, thickened or not;

stamens 5–8.

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 or exserted from perianth, light to dark brown, ovate, (2–)3-gonous, 1.2–4.2 mm, faces subequal or unequal, apex not beaked, edges slightly concave, dull, usually coarsely striate-tubercled, sometimes obscurely tubercled; late-season achenes common or not, 2–5 mm.

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 aviculare

Polygonum glaucum

Phenology Flowering Jul–Nov.
Habitat Coastal beaches, sand dunes, margins of salt ponds
Elevation 0-10 m (0-0 ft)
Distribution
from FNA
AK; AL; AR; AZ; CA; CO; CT; DC; DE; FL; GA; IA; ID; IL; IN; KS; KY; LA; MA; MD; ME; MI; MN; MO; MS; MT; NC; ND; NE; NH; NJ; NM; NV; NY; OH; OK; OR; PA; RI; SC; SD; TN; TX; UT; VA; VT; WA; WI; WV; WY; AB; BC; MB; NB; NL; NS; NT; ON; PE; QC; SK; YT; nearly worldwide
[WildflowerSearch map]
[BONAP county map]
from FNA
CT; DC; DE; FL; GA; MA; MD; NC; NJ; NY; RI; SC; VA
[BONAP county map]
Discussion

Subspecies 7+ (6 in the flora).

Polygonum aviculare is a taxonomically controversial polyploid complex of selfing annuals. Although members of the complex have been considered inbreeders, they possess some structures that make cross pollination possible. Cleistogamous and chasmogamous flowers, heterostyly, protandry, and the capacity to secrete nectar suggest an ancestral mixed-mating system. Isoenzyme studies showed that the complex has an allopolyploid origin (P. Meerts et al. 1998) and has evolved as a swarm of inbreeding lines (“Jordanons”) (J. Gasquez et al. 1978). The six subspecies included here have been treated variously (T. Karlsson 2000; M. Costea and F. J. Tardif 2003). Complex intergradation patterns among them make their recognition at the species level impractical. Multivariate analysis and isoenzyme studies show that populations with intermediate characteristics may occur (Meerts et al. 1990, 1998). Except for subsp. boreale, which occurs in Greenland and Labrador, all subspecies are partially sympatric and their distributions have been influenced greatly by humans.

(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.)

Key
1. Perianth tubes 40-57% of perianth length
→ 2
1. Perianth tubes (15-)20-40(-42)% of perianth length. [3. Shifted to left margin.—Ed.]
→ 3
2. Tepals green or reddish brown, margins white, veins unbranched
subsp. depressum
2. Tepals green, margins usually pink or red, rarely white, veins branched
subsp. neglectum
3. Perianths 3.3-5.5 mm; achenes 2.5-4.2 mm
→ 4
3. Perianths 1.9-3.6 mm; achenes 1.2-2.8(-3) mm
→ 5
4. Plants heterophyllous; leaf blades elliptic to oblanceolate; tepals oblong, cucullate in fruit; cymes aggregated at tips of stems and branchs; broad distribution in North America
subsp. aviculare
4. Plants homophyllous or subheterophyllous; leaf blades obovate-spatulate or oblanceolate; tepals obovate, flat or curved outward in fruit; cymes ± uniformly distributed; Greenland, Newfoundland and Labrador
subsp. boreale
5. Ocreae with distal parts relatively persistent, silvery; perianths 0.9-1.3(-1.5) times as long as wide, outer tepals pouched at base
subsp. buxiforme
5. Ocreae soon disintegrating into persistent fibers or leaving almost no fibrous remains; perianths 1.5-2.9 times as long as wide; outer tepals not pouched at base
→ 6
6. Leaf blades (6-)10-20 mm wide, 2-4.5 times as long as wide; cymes 3-8-flowered, aggregated at tips of stems and branches; achenes enclosed in or barely exserted from perianth
subsp. aviculare
6. Leaf blades 0.5-6.8(-8) mm wide, (3.4-)4.2-15(-19) times as long as wide; cymes 1-3(-5)-flowered, uniformly distributed along stems and branches; achenes usually exserted from perianth
→ 7
7. Ocreae 4-8 mm, veins inconspicuous, distal parts leaving almost no fibrous remains; lateral veins of leaf blades visible but not raised adaxially
subsp. neglectum
7. Ocreae (6-)8-12 mm, veins conspicuous, distal parts disintegrating into persistent fibers; lateral veins of leaf blades raised adaxially
subsp. rurivagum
Source FNA vol. 5, p. 556. FNA vol. 5, p. 553.
Parent taxa Polygonaceae > subfam. Polygonoideae > Polygonum > sect. Polygonum Polygonaceae > subfam. Polygonoideae > Polygonum > sect. Polygonum
Sibling taxa
P. achoreum, P. argyrocoleon, P. austiniae, P. bidwelliae, 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
Subordinate taxa
P. aviculare subsp. aviculare, P. aviculare subsp. boreale, P. aviculare subsp. buxiforme, P. aviculare subsp. depressum, P. aviculare subsp. neglectum, P. aviculare subsp. rurivagum
Name authority Linnaeus: Sp. Pl. 1: 362. (1753) Nuttall: Gen. N. Amer. Pl. 1: 254. (1818)
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