Polygonum aviculare |
Polygonum spergulariiforme |
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birdweed, common knotgrass, common knotweed, doorweed, dooryard knotweed, knotgrass, knotweed, lowgrass, pigweed, prostrate knotweed, renouée des oiseaux, yard knotweed |
autumn knotweed, fall knotweed, scatter knotweed, spurry 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, divaricately branched, not wiry, 5–50 cm, usually papillose-scabrid-ulous, rarely glabrescent. |
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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 usually caducous, distal leaves abruptly reduced to bracts, articulated to ocreae; ocrea 8–12 mm, papillose-scabridulous, proximal part cylindric, distal part disintegrating into a few persistent fibers; petiole 0.1–2 mm; blade 1-veined, not pleated, linear to lanceolate, 35–60 × 1–3 mm, margins flat or narrowly revolute, smooth or papillose-denticulate, apex acute, 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, dense; cymes crowded, ± overlapping at branch tips, 2–5-flowered. |
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Pedicels | enclosed in or exserted from ocreae, 1.5–5 mm. |
enclosed in or slightly exserted from ocreae, erect to spreading, 0.5–2 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 mm; tube 9–17% of perianth length; tepals overlapping, uniformly pink or white, petaloid, oblong-obovate, cucullate, navicular in distal 1/4, apex rounded; midveins branched; 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, narrowly elliptic or elliptic-lanceolate to narrowly ovate, 3–5 mm, faces subequal, shiny, smooth to striate-tubercled. |
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Polygonum aviculare |
Polygonum spergulariiforme |
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Phenology | Flowering Jun–Oct. | |||||||||||||||||||||||||||||
Habitat | Moist to dry, open rocky places, including serpentine | |||||||||||||||||||||||||||||
Elevation | 10-2000 m (0-6600 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; ID; MT; OR; 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. douglasii subsp. spergulariiforme, P. emaciatum | |||||||||||||||||||||||||||||
Name authority | Linnaeus: Sp. Pl. 1: 362. (1753) | Meisner ex Small: Bull. Torrey Bot. Club 19: 366. (1892) | ||||||||||||||||||||||||||||
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