Polygonum aviculare |
Polygonum aviculare subsp. depressum |
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birdweed, common knotgrass, common knotweed, doorweed, dooryard knotweed, knotgrass, knotweed, lowgrass, pigweed, prostrate knotweed, renouée des oiseaux, yard knotweed |
common knotweed, oval-leaf knotweed, prostrate knotweed, renouée à petits fruits |
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Habit | Plants green or bluish green, green after drying, sometimes whitish from powdery mildew, homophyllous or heterophyllous. | Plants green, homophyllous or subheterophyllous. | ||||||||||||||||||||||||||||
Stems | prostrate to erect, branched, flexuous, 5–200 cm. |
3–15, prostrate to ascending, mat-forming, branched at most nodes, proximal branches divaricate, (5–)10–50(–100) cm. |
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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 with proximal part cylindric to funnelform, either short, 3–5.5 mm, with distal part soon disintegrating and leaving almost no fibrous remains, or long, 7–12 mm, with distal part with veins inconspicuous, membranous, margins ± lacerate, overlapping towards apices of stems and branches; petiole 0.5–3 mm; blade green, lateral veins visible but not raised abaxially, elliptic to narrowly elliptic or oblanceolate, (6.2–)8–27(–35) × (1.4–)2–7(–10) mm, 2.8–5.7(–6.5) times as long as wide, apex obtuse or acute, rarely longitudinally striate; stem leaves 1–2.3(–3.4) times as long as branch leaves. |
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Inflorescences | axillary; cymes uniformly distributed or aggregated at tips of stems and branches, 1–6(–8)-flowered. |
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Pedicels | enclosed in or exserted from ocreae, 1.5–5 mm. |
enclosed in ocreae, 1–2.5 mm. |
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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. |
perianth (1.8–)2–3.4(–4) mm, 1.5–2.9 times as long as wide; tube 40–57% of perianth length; tepals overlapping but spreading slightly in fruit, green or reddish brown with white margins, oblong, flat or obscurely cucullate in fruit, outer tepals not pouched at base; midveins unbranched, thin to moderately thickened; stamens 5–7. |
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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. |
usually slightly exserted from perianth, dark brown, ovate, (2–)3-gonous, 1.5–2.7(–3) mm, faces evidently unequal, flat to concave, apex straight or slightly bent toward narrow face, almost smooth, roughened, or coarsely striate-tubercled; late-season achenes common, 2.5–4.5 mm. |
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Cymes | uniformly distributed or, sometimes, crowded at tips of branches, 2–7-flowered. |
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2n | = 40, 60. |
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Polygonum aviculare |
Polygonum aviculare subsp. depressum |
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Phenology | Flowering May–Nov. | |||||||||||||||||||||||||||||
Habitat | Fields, uncultivated areas, waste places, roadsides | |||||||||||||||||||||||||||||
Elevation | 0-2500 m (0-8200 ft) | |||||||||||||||||||||||||||||
Distribution |
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
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AK; AL; AR; AZ; CA; CO; CT; DE; FL; GA; IA; ID; IL; IN; KS; KY; LA; MA; MD; ME; MI; MN; MO; 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; Europe [Introduced in North America] |
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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 montereyense is a distinctive morphotype that may deserve infraspecific recognition. Plants referable to it have ocreae 8–13 mm, with distal parts silvery, persistent, entire or slightly lacerate, overlapping, and few-veined. Apparently, this type is restricted to California. Plants referable to P. arenastrum in the narrow sense are the most commonly encountered form of the subspecies in North America. Subspecies depressum has been reported from Greenland and St. Pierre and Miquelon; those reports have not been confirmed. (Discussion copyrighted by Flora of North America; reprinted with permission.) |
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Key |
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Source | FNA vol. 5, p. 556. | FNA vol. 5, p. 559. | ||||||||||||||||||||||||||||
Parent taxa | Polygonaceae > subfam. Polygonoideae > Polygonum > sect. Polygonum | Polygonaceae > subfam. Polygonoideae > Polygonum > sect. Polygonum > Polygonum aviculare | ||||||||||||||||||||||||||||
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Synonyms | P. aviculare var. depressum, P. aequale, P. arenastrum, P. aviculare subsp. aequale, P. aviculare subsp. calcatum, P. aviculare subsp. microspermum, P. calcatum, P. microspermum, P. montereyense | |||||||||||||||||||||||||||||
Name authority | Linnaeus: Sp. Pl. 1: 362. (1753) | (Meisner) Arcangeli: Comp. Fl. Ital., 583. (1882) | ||||||||||||||||||||||||||||
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