Polygonum aviculare
Polygonum
birdweed, common knotgrass, common knotweed, doorweed, dooryard knotweed, knotgrass, knotweed, lowgrass, pigweed, prostrate knotweed, renouée des oiseaux, yard knotweed
doorweed, knotweed, smartweed
prostrate to erect, branched, flexuous, 5–200 cm.
prostrate to erect, glabrous, smooth or sometimes papillous-scabridulous.
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.
cauline, alternate (opposite in P. humifusum), petiolate or sessile;
ocrea with distal part persistent, often hyaline, white or silvery, 2-lobed, chartaceous, glabrous, disintegrating into fibers, or disintegrating completely;
petiole base articulated with ocrea or not;
blade linear, lanceolate, elliptic, ovate, or subround, margins entire.
axillary;
cymes uniformly distributed or aggregated at tips of stems and branches, 1–6(–8)-flowered.
axillary or axillary and terminal, spikelike, or flowers solitary;
peduncle absent.
enclosed in or exserted from ocreae, 1.5–5 mm.
present or absent.
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.
bisexual, 1–7(–10) per ocreate fascicle, base not stipelike;
perianth nonaccrescent, white or greenish white to pink, campanulate to urceolate, glabrous;
tepals 5, connate 3–70% of their length, petaloid or sepaloid, monomorphic or, rarely, dimorphic, the inner usually flat, the outer flat or sometimes keeled and cucullate distally, sometimes of different length than the inner;
stamens 3–8 (some may be reduced to staminodes);
filaments distinct, free or adnate to perianth tube, glabrous;
anthers whitish yellow, pink to purple or orange-pink, elliptic to oblong;
styles (2–)3, mostly spreading, distinct or connate proximally;
stigmas 2–3, capitate.
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.
included or exserted, yellow-green, brown, or black, unwinged, (2–)3-gonous, glabrous.
embryo curved.
= 10.
Polygonum aviculare
Polygonum
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.)
Species ca. 65 (33 in the flora).
Two sections of Polygonum are recognized here. Section Polygonum is nearly cosmopolitan and best represented in north-temperate regions; sect. Duravia comprises species restricted to North America. K. Haraldson (1978) recognized both sections based on differences in stem morphology, petiole structure, and pollen morphology. J. C. Hickman (1984) described sect. Monticola and included in it species of sect. Duravia occurring mostly in montane habitats, with leaves articulated to the ocreae, one-veined, and not mucronate, proximal leaves lanceolate to round, and styles connate at their bases and neither hardened nor persistent. L.-P. Ronse Decraene and J. R. Akeroyd (1988) and L.-P. Ronse Decraene et al. (2000) included sect. Duravia in sect. Polygonum based on floral and fruit characters.
Similarities in floral structure, fruit anatomy, and pollen morphology have been noted between Polygonella with Polygonum (L.-P. Ronse Decraene et al. 2000). Based on evidence from comparative morphological studies, Ronse Decraene et al. (2004) included Polygonella in sect. Duravia of Polygonum.
Four introduced taxa of sect. Polygonum that were collected in the flora area at the end of the nineteenth century and beginning of the twentieth century appear not to have persisted here and are not included in the keys. Polygonum arenarium Waldstein & Kitaibel and P. bellardii Allioni were reported by B. L. Robinson (1902) from Rhode Island and Massachusetts, respectively. The former resembles P. patulum but has open flowers. Polygonum bellardii is discussed below under P. ramosissimum. Polygonum polycnemoides Jaubert & Spach and P. humifusum C. Merck ex K. Koch subsp. humifusum were reported by J. F. Brenckle (1941). The former was collected in New York City in 1894 and in Idaho in 1940. It differs from all other Polygonum species in having a tube 55–70% of the perianth length. Polygonum humifusum subsp. humifusum is discussed below under P. humifusum subsp. caurianum.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
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 |
Key to the Sections of Polygonum
1. Stems distinctly and ± regularly 8-16-ribbed; leaf blade venation pinnate, secondary veins conspicuous; anthers whitish yellow; nearly worldwide | sect. Polygonum |
1. Stems 4-gonous, ribs obscure or absent; leaf blade venation parallel, secondary veins not conspicuous; anthers pink to purple; mostly w North America | sect. Duravia |
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