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

striped knotweed, Texas knotweed

Habit Herbs. Plants perennial, light green, heterophyllous; rhizomes brown, 0.7–3 cm diam.
Stems

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

erect to ascending, sparingly branched in distal 1/2, not wiry, 25–60 cm.

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 6–12 mm, proximal part cylindric, distal part soon disintegrating into brown fibers, later leaving almost no fibrous remains;

petiole 0–2 mm;

blade light green, linear-lanceolate to oblanceolate, 8–35 × 2–8 mm, margins flat, apex acute or obtuse;

stem leaves 2.1–4 times as long as adjacent branch leaves;

distal leaves sharply reduced, not overtopping flowers (shorter than or equaling flowers).

Inflorescences

axillary and terminal, spikelike, elongate;

cymes spaced along branches, 2–5-flowered.

axillary and terminal, spikelike;

cymes in distal nodes, 2–6-flowered.

Pedicels

exserted from ocreae, reflexed, 0.5–1 mm.

exserted from ocreae, 2–4 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.

semi-open;

perianth 2–3.5 mm;

tube 18–25% of perianth length;

tepals overlapping, green with white or sometimes pink margins, petaloid, not keeled, oblong to obovate, cucullate;

midveins usually unbranched;

stamens 7–8.

Achenes

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

enclosed in perianth, brown, ovate, 3-gonous, (1.6–)1.8–2.6(–3) mm, faces subequal or unequal, apex not beaked, edges concave, shiny, smooth or roughened; late-season achenes common, 4–6 mm.

Polygonum majus

Polygonum striatulum

Phenology Flowering May–Aug. Flowering Dec–Mar or Jun–Oct.
Habitat Dry plains, meadows, sometimes on serpentine Seasonal moist places, sterile prairies, granitic soils
Elevation 500-2000 m (1600-6600 ft) 100-700 m (300-2300 ft)
Distribution
from FNA
CA; CO; ID; NV; OR; UT; WA; WY; BC
[WildflowerSearch map]
[BONAP county map]
from FNA
TX
[BONAP county map]
Discussion

Plants with leaves less-conspicuously veined, flowering August to October, and growing in seasonally moist habitats in central and western Texas are recognized by some authors as Polygonum texense or P. striatulum var. texense (M. Costea and F. J. Tardif 2003).

(Discussion copyrighted by Flora of North America; reprinted with permission.)

Source FNA vol. 5, p. 570. FNA vol. 5, p. 550.
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. plebeium, P. polygaloides, P. ramosissimum, P. sawatchense, P. shastense, P. spergulariiforme, P. tenue, P. utahense
Synonyms P. coarctatum var. majus, P. douglasii subsp. majus P. striatulum var. texense, P. texense
Name authority (Meisner) Piper: Fl. Palouse Reg., 63. (1901) B. L. Robinson: Proc. Boston Soc. Nat. Hist. 31: 263. (1904)
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