Polygonum aviculare |
Polygonum majus |
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birdweed, common knotgrass, common knotweed, doorweed, dooryard knotweed, knotgrass, knotweed, lowgrass, pigweed, prostrate knotweed, renouée des oiseaux, yard knotweed |
large Douglas' knotweed, large knotweed, Palouse knotweed, wiry knotweed |
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Habit | Plants green or bluish green, green after drying, sometimes whitish from powdery mildew, homophyllous or heterophyllous. | Herbs. | ||||||||||||||||||||||||||||
Stems | prostrate to erect, branched, flexuous, 5–200 cm. |
erect, green, simple or branched, ± wiry, 15–60 cm, usually papillose-scabridulous. |
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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. |
uniformly distributed, articulated to ocreae, basal leaves often caducous, distal leaves abruptly reduced to bracts, articulated to ocreae; ocrea 5–12 mm, glabrous or papillose-scabridulous, proximal part cylindric, distal part lacerate or disintegrating into fibers; petiole 0.1–2 mm; blade 1-veined, not pleated, linear to narrowly oblong or lanceolate, 15–70 × 2–8 mm, margins revolute, papillose-denticulate, apex acute or mucronate. |
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Inflorescences | axillary; cymes uniformly distributed or aggregated at tips of stems and branches, 1–6(–8)-flowered. |
axillary and terminal, spikelike, elongate; cymes spaced along branches, 2–5-flowered. |
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Pedicels | enclosed in or exserted from ocreae, 1.5–5 mm. |
exserted from ocreae, reflexed, 0.5–1 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. |
open or semi-open; perianth (3.5–)4–5 mm; tube 9–17% of perianth length; tepals overlapping, uniformly white to pink, petaloid, oblong to oblong-obovate, cucullate, navicular in distal 1/4, apex rounded; midveins unbranched or with short lateral branches; stamens 8. |
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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. |
enclosed in perianth, black, elliptic, 3.5–5 mm, faces subequal, shiny or dull, smooth or striate-tubercled. |
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Polygonum aviculare |
Polygonum majus |
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Phenology | Flowering May–Aug. | |||||||||||||||||||||||||||||
Habitat | Dry plains, meadows, sometimes on serpentine | |||||||||||||||||||||||||||||
Elevation | 500-2000 m (1600-6600 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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CA; CO; ID; NV; OR; UT; WA; WY; BC
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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.) |
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Key |
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Source | FNA vol. 5, p. 556. | FNA vol. 5, p. 570. | ||||||||||||||||||||||||||||
Parent taxa | Polygonaceae > subfam. Polygonoideae > Polygonum > sect. Polygonum | Polygonaceae > subfam. Polygonoideae > Polygonum > sect. Duravia | ||||||||||||||||||||||||||||
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Synonyms | P. coarctatum var. majus, P. douglasii subsp. majus | |||||||||||||||||||||||||||||
Name authority | Linnaeus: Sp. Pl. 1: 362. (1753) | (Meisner) Piper: Fl. Palouse Reg., 63. (1901) | ||||||||||||||||||||||||||||
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