Polygonum aviculare |
Polygonum douglasii |
|||||||||||||||||||||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
birdweed, common knotgrass, common knotweed, doorweed, dooryard knotweed, knotgrass, knotweed, lowgrass, pigweed, prostrate knotweed, renouée des oiseaux, yard knotweed |
Douglas' knotweed, renouée de Douglas |
|||||||||||||||||||||||||||||
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, not wiry, 5–80 cm, glabrous or sparsely papillose-scabridulous. |
||||||||||||||||||||||||||||
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 caducous, distal leaves abruptly reduced to bracts; ocrea 6–12 mm, glabrous or minutely papillose-scabridulous, proximal part cylindric, distal part hyaline, lacerate; petiole 0.1–2 mm; blade 1-veined, not pleated, linear, narrow-oblong, or oblanceolate, 15–55 × 2–8(–12) mm, margins revolute, smooth or papillose-denticulate; apex acute to mucronate. |
||||||||||||||||||||||||||||
Inflorescences | axillary; cymes uniformly distributed or aggregated at tips of stems and branches, 1–6(–8)-flowered. |
axillary and terminal, spikelike, elongate; cymes widely spaced along branches, 2–4-flowered. |
||||||||||||||||||||||||||||
Pedicels | enclosed in or exserted from ocreae, 1.5–5 mm. |
mostly exserted from ocreae, reflexed, 2–6 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. |
closed; perianth 3–4.5 mm; tube 20–28% of perianth length; tepals overlapping, green to tannish with white or pink margins, petaloid, oblong, cucullate, navicular, apex rounded; midveins usually branched, rarely 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. |
enclosed in perianth, black, elliptic or oblong to ovate, 3–4(–4.5) mm, faces subequal, shiny or dull, smooth or minutely striate-tubercled. |
||||||||||||||||||||||||||||
Polygonum aviculare |
Polygonum douglasii |
|||||||||||||||||||||||||||||
Phenology | Flowering Jun–Oct. | |||||||||||||||||||||||||||||
Habitat | Dry, often disturbed places, rock outcrops, sandy ground | |||||||||||||||||||||||||||||
Elevation | 300-3000 m (1000-9800 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
|
AZ; CA; CO; IA; ID; MI; MN; MT; NE; NH; NM; NV; NY; OR; SD; UT; VA; VT; WA; WY; AB; BC; MB; ON; QC; SK; YT
|
||||||||||||||||||||||||||||
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.) |
Five taxa that have been included in Polygonum douglasii (E. Murray 1982; J. C. Hickman 1984; J. T. Kartesz and K. N. Gandhi 1990) are treated here as distinct species: P. austiniae, P. majus, P. nuttallii, P. sawatchense, and P. spergulariiforme. Hickman noted extensive intergradation and numerous intermediate specimens among those sympatric elements, but qualitative or quantitative characters allow reliable discrimination in most cases (M. Costea and F. J. Tardif 2005), and species are here circumscribed similar to C. L. Hitchcock (1964). Greene described var. latifolium as having leaf blades and achenes broader than those of var. douglasii. C. L. Hitchcock (1964) recognized the former, but the characters used to distinguish it appear to vary continuously, and reliable separation is not possible. (Discussion copyrighted by Flora of North America; reprinted with permission.) |
||||||||||||||||||||||||||||
Key |
|
|||||||||||||||||||||||||||||
Source | FNA vol. 5, p. 556. | FNA vol. 5, p. 567. | ||||||||||||||||||||||||||||
Parent taxa | Polygonaceae > subfam. Polygonoideae > Polygonum > sect. Polygonum | Polygonaceae > subfam. Polygonoideae > Polygonum > sect. Duravia | ||||||||||||||||||||||||||||
Sibling taxa | ||||||||||||||||||||||||||||||
Subordinate taxa | ||||||||||||||||||||||||||||||
Synonyms | P. douglasii var. latifolium, P. emaciatum, P. montanum, P. tenue var. commune, P. tenue var. latifolium | |||||||||||||||||||||||||||||
Name authority | Linnaeus: Sp. Pl. 1: 362. (1753) | Greene: Bull. Calif. Acad. Sci. 1: 125. (1885) | ||||||||||||||||||||||||||||
Web links |
|
|