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Bidwell knotweed, Bidwell's knotweed

bushy knotweed, yellow knotweed, yellow-flower knotweed

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

erect, green, simple or divaricately branched, ± wiry, 2–20 cm, minutely papillose-scabridulous.

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

Leaves

crowded at branch tips, not articulated to ocreae, basal leaves caducous or persistent, distal leaves abruptly reduced to bracts;

ocrea 8–13 mm, papillose-scabridulous, proximal part cylindric, distal part overlapping and obscuring leaves and flowers, silvery, entire or shallowly dentate;

petiole absent;

blade 3-veined, without pleats, linear, 5–15(–20) × 0.5–1.5(–2) mm, margins revolute, papillose-denticulate, apex spine-tipped.

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.

Inflorescences

axillary;

cymes in distal axils, 1-flowered.

axillary or axillary and terminal, spikelike;

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

Pedicels

absent.

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

Flowers

closed;

perianth 2–3 mm;

tube 10–18% of perianth length;

tepals overlapping, pink with pink or white margins, petaloid, elliptic, navicular, apex acute to acuminate;

midveins unbranched;

stamens 8.

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).

Achenes

enclosed in perianth at maturity, light brown to brown, ovate-elliptic, 1.8–2.3 mm, faces subequal, shiny, smooth.

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.

Polygonum bidwelliae

Polygonum ramosissimum

Phenology Flowering May–Jun.
Habitat Thin volcanic soils, chaparral, montane woodland valleys, grasslands
Elevation 60-1200 m (200-3900 ft)
Distribution
from FNA
CA
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[BONAP county map]
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]
Discussion

Polygonum bidwelliae occurs in the Cascade Range and northeastern Sacramento Valley in Butte, Shasta, and Tehama counties.

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

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. 565. FNA vol. 5, p. 551.
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. 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
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
Subordinate taxa
P. ramosissimum subsp. prolificum, P. ramosissimum subsp. ramosissimum
Name authority S. Watson: Proc. Amer. Acad. Arts 14: 294. (1879) Michaux: Fl. Bor.-Amer. 1: 237. (1803)
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