The green links below add additional plants to the comparison table. Blue links lead to other Web sites.
enable glossary links

Parry's knotweed, Parry's or prickly knotweed, prickly knotweed

birdweed, common knotgrass, common knotweed, doorweed, dooryard knotweed, knotgrass, knotweed, lowgrass, pigweed, prostrate knotweed, renouée des oiseaux, yard knotweed

Habit Herbs, compact, often cushion-like. Plants green or bluish green, green after drying, sometimes whitish from powdery mildew, homophyllous or heterophyllous.
Stems

erect, green-brown, simple or branched from base, not wiry, 2–5(–8) cm, glabrous.

prostrate to erect, branched, flexuous, 5–200 cm.

Leaves

± uniformly distributed, dense, not articulated to ocreae, basal leaves ± persistent, distal leaves gradually reduced to bracts;

ocrea 2–4(–5) mm, glabrous, proximal part cylindric, distal part deeply lacerate, disintegrating into white, curled fibers;

petiole absent;

blade 3-veined, without pleats, linear-lanceolate, subulate, 5–13(–20) × 0.4–1 mm, margins revolute, smooth, apex spine-tipped.

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.

Inflorescences

axillary;

cymes in most axils, 1-flowered.

axillary;

cymes uniformly distributed or aggregated at tips of stems and branches, 1–6(–8)-flowered.

Pedicels

absent.

enclosed in or exserted from ocreae, 1.5–5 mm.

Flowers

closed;

perianth 1.5–2(–2.5) mm;

tube 6–15% of perianth length;

tepals overlapping, usually reddish with white margins, petaloid, oblong, navicular, apex acute;

midveins unbranched;

stamens 8.

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.

Achenes

slightly exserted from perianth at maturity, dark brown, ovate, 1.2–1.6(–2) mm, faces subequal, shiny, smooth.

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.

Polygonum parryi

Polygonum aviculare

Phenology Flowering May–July.
Habitat Vernally moist, open, sandy or rocky places
Elevation 500-2000 m (1600-6600 ft)
Distribution
from FNA
CA; WA
[WildflowerSearch map]
[BONAP county map]
from FNA
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
[WildflowerSearch map]
[BONAP county map]
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.)

Key
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
Source FNA vol. 5, p. 563. FNA vol. 5, p. 556.
Parent taxa Polygonaceae > subfam. Polygonoideae > Polygonum > sect. Duravia Polygonaceae > subfam. Polygonoideae > Polygonum > sect. Polygonum
Sibling taxa
P. achoreum, P. argyrocoleon, P. austiniae, P. aviculare, P. bidwelliae, P. bolanderi, P. californicum, P. cascadense, P. douglasii, P. engelmannii, P. erectum, P. fowleri, P. glaucum, P. heterosepalum, P. hickmanii, P. humifusum, P. majus, P. marinense, P. minimum, P. nuttallii, P. oxyspermum, P. paronychia, P. patulum, P. plebeium, P. polygaloides, P. ramosissimum, P. sawatchense, P. shastense, P. spergulariiforme, P. striatulum, P. tenue, P. utahense
P. achoreum, P. argyrocoleon, P. austiniae, P. bidwelliae, P. bolanderi, P. californicum, P. cascadense, P. douglasii, P. engelmannii, P. erectum, P. fowleri, P. glaucum, P. heterosepalum, P. hickmanii, P. humifusum, P. majus, P. marinense, P. minimum, P. nuttallii, P. oxyspermum, P. paronychia, P. parryi, P. patulum, P. plebeium, P. polygaloides, P. ramosissimum, P. sawatchense, P. shastense, P. spergulariiforme, P. striatulum, P. tenue, P. utahense
Subordinate taxa
P. aviculare subsp. aviculare, P. aviculare subsp. boreale, P. aviculare subsp. buxiforme, P. aviculare subsp. depressum, P. aviculare subsp. neglectum, P. aviculare subsp. rurivagum
Name authority Greene: Bull. Torrey Bot. Club 8: 99. (1881) Linnaeus: Sp. Pl. 1: 362. (1753)
Web links