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large Douglas' knotweed, large knotweed, Palouse knotweed, wiry knotweed

common knotweed

Habit Herbs. Plants bluish green, homophyllous.
Stems

erect, green, simple or branched, ± wiry, 15–60 cm, usually papillose-scabridulous.

prostrate, much-branched from base, not wiry, 10–40 cm, papillose-scabridulous.

Leaves

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.

ocrea 1-veined, 2.5–3 mm, proximal part cylindric, distal part laciniate;

petiole 0–1 mm;

blade bluish green, narrowly elliptic or oblanceolate, 5–16 × 1–4 mm, margins flat, apex obtuse or acute, papillose-scabridulous;

stem leaves 1–1.5(–2) times longer than adjacent branch leaves, distal leaves overtopping flowers.

Inflorescences

axillary and terminal, spikelike, elongate;

cymes spaced along branches, 2–5-flowered.

axillary;

cymes uniformly distributed, 3–6-flowered.

Pedicels

exserted from ocreae, reflexed, 0.5–1 mm.

exserted from ocreae, 3–5 mm.

Flowers

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.

closed;

perianth 1–1.5 mm;

tube 12–27% of perianth length;

tepals overlapping, green with white or pink margins, petaloid, not keeled, elliptic, cucullate;

midveins unbranched, thickened;

stamens 5.

Achenes

enclosed in perianth, black, elliptic, 3.5–5 mm, faces subequal, shiny or dull, smooth or striate-tubercled.

enclosed in perianth, black-brown, broadly ovate, 2–3-gonous, 1.5–2 mm, faces subequal, apex not beaked, edges concave, shiny, smooth; late-season achenes common, 2–4 mm.

2n

= 20.

Polygonum majus

Polygonum plebeium

Phenology Flowering May–Aug. Flowering May–Oct.
Habitat Dry plains, meadows, sometimes on serpentine Disturbed sites
Elevation 500-2000 m (1600-6600 ft) 50-500 m (200-1600 ft)
Distribution
from FNA
CA; CO; ID; NV; OR; UT; WA; WY; BC
[WildflowerSearch map]
[BONAP county map]
from FNA
ID; e Africa; s Asia; Australia [Introduced in North America]
[BONAP county map]
Source FNA vol. 5, p. 570. 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. 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
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. parryi, P. patulum, P. polygaloides, P. ramosissimum, P. sawatchense, P. shastense, P. spergulariiforme, P. striatulum, P. tenue, P. utahense
Synonyms P. coarctatum var. majus, P. douglasii subsp. majus
Name authority (Meisner) Piper: Fl. Palouse Reg., 63. (1901) R. Brown: Prodr., 420. (1810)
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