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bushy knotweed, yellow knotweed, yellow-flower knotweed

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

Habit Plants yellowish green or bluish green, (dark brown to black after drying in subsp. prolificum), heterophyllous or homophyllous. Herbs.
Stems

erect, usually profusely branched in distal 1/2, not wiry, 10–100(–200) cm.

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

Leaves

ocrea 6–12(–15) mm, proximal part cylindric, distal part silvery, soon disintegrating into persistent brown fibers;

petiole 2–4 mm;

blade variable, light yellowish green to bluish green, proximal often caducous, narrowly elliptic, lanceolate, or oblanceolate, rarely ovate, 8–70 × 4–18(–35) mm, margins flat, apex acute to acuminate or obtuse;

distal leaves, either overtopping or shorter than or equaling flowers.

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.

Inflorescences

axillary or axillary and terminal, spikelike;

cymes uniformly distributed or crowded toward tips of branches, 2–5-flowered.

axillary and terminal, spikelike, elongate;

cymes spaced along branches, 2–5-flowered.

Pedicels

enclosed in or exserted from ocreae, 1–6 mm.

exserted from ocreae, reflexed, 0.5–1 mm.

Flowers

closed;

perianth (2–)2.2–3.6(–4) mm;

tube 20–38% of perianth length;

tepals overlapping, greenish yellow with greenish yellow or yellow, rarely pink or white, margins, petaloid or sepaloid, not keeled, elliptic to oblong, cucullate;

midveins thickened or not;

stamens 3–6(–8).

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.

Achenes

enclosed in or exserted from perianth, dark brown, ovate, 3-gonous, 1.6–3.5 mm, faces subequal, concave, apex not beaked, edges straight, shiny or dull, usually smooth to roughened, sometimes uniformly or obscurely tubercled; late-season achenes common, 4–15 mm.

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

Polygonum ramosissimum

Polygonum majus

Phenology Flowering May–Aug.
Habitat Dry plains, meadows, sometimes on serpentine
Elevation 500-2000 m (1600-6600 ft)
Distribution
from FNA
AR; AZ; CA; CO; CT; DE; 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; NS; NT; ON; PE; QC; SK
[WildflowerSearch map]
[BONAP county map]
from FNA
CA; CO; ID; NV; OR; UT; WA; WY; BC
[WildflowerSearch map]
[BONAP county map]
Discussion

Subspecies 2 (2 in the flora).

Polygonum ramosissimum exhibits considerable morphological complexity and is similar in difficulty to the P. aviculare complex. Further research is necessary to understand the infraspecific variability of this species (M. Costea and F. J. Tardif 2003b).

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

Key
1. Plants heterophyllous, usually yellowish green when fresh or dried; apices of leaf blades acute to acuminate; pedicels 2.5-6 mm
subsp. ramosissimum
1. Plants homophyllous, bluish green when fresh, dark brown or black after drying; apices of leaf blades rounded or obtuse; pedicels 1-2 mm
subsp. prolificum
Source FNA vol. 5, p. 551. FNA vol. 5, p. 570.
Parent taxa Polygonaceae > subfam. Polygonoideae > Polygonum > sect. Polygonum Polygonaceae > subfam. Polygonoideae > Polygonum > sect. Duravia
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. parryi, P. patulum, P. plebeium, P. polygaloides, 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. 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. ramosissimum subsp. prolificum, P. ramosissimum subsp. ramosissimum
Synonyms P. coarctatum var. majus, P. douglasii subsp. majus
Name authority Michaux: Fl. Bor.-Amer. 1: 237. (1803) (Meisner) Piper: Fl. Palouse Reg., 63. (1901)
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