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beak-seed knotweed, Blake's knotweed, leathery knotweed, renouée coriace, striate knotweed

Bidwell knotweed, Bidwell's knotweed

Habit Plants light green (often covered with whitish powdery mildew), homophyllous or, sometimes, heterophyllous. Herbs.
Stems

erect when young, decumbent or prostrate later, moderately branched especially from base, not wiry, 50–70 cm.

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

Leaves

ocreae 5–12 mm, proximal part cylindric, distal part soon disintegrating into brown fibers;

petiole 0.3–1.5 mm;

blade light yellowish green, elliptic to obovate, 8–35 × 3–15 mm, margins flat, apex rounded;

stem leaves 1–2.1(–3) times longer than branch leaves;

distal leaves overtopping flowers.

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.

Inflorescences

axillary, cymes in axils of most leaves and toward tips of stems and branchs, 1–3(–5)-flowered.

axillary;

cymes in distal axils, 1-flowered.

Pedicels

enclosed in ocreae, 1.3–1.8(–2) mm.

absent.

Flowers

closed;

perianth 2.6–4 mm;

tube 40–55% of perianth length;

tepals incurved, yellow-green with yellow to green, rarely pinkish, margins, sepaloid, ± keeled, narrowly oblong, cucullate;

midveins unbranched, moderately to heavily thickened, tepals appearing keeled;

stamens 5–8.

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.

Achenes

enclosed in perianth, yellow-green to tan, ovate, 3-gonous, 2.4–3.5 mm, faces unequal, apex not beaked, edges concave or nearly straight, dull, uniformly tubercled; late-season achenes common, 3–5 mm.

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

2n

= 40, 60.

Polygonum achoreum

Polygonum bidwelliae

Phenology Flowering Jul–Sep. Flowering May–Jun.
Habitat Disturbed areas, roadsides, sidewalks, edges of cultivated fields Thin volcanic soils, chaparral, montane woodland valleys, grasslands
Elevation 10-800 m (0-2600 ft) 60-1200 m (200-3900 ft)
Distribution
from FNA
AK; CO; CT; IA; ID; IL; IN; KS; ME; MI; MN; MO; MT; ND; NE; NV; NY; OH; OR; SD; UT; VT; WA; WI; WV; WY; AB; BC; MB; NB; NS; NT; ON; QC; SK; YT
[WildflowerSearch map]
[BONAP county map]
from FNA
CA
[WildflowerSearch map]
[BONAP county map]
Discussion

Polygonum achoreum frequently is confused with P. erectum. It can be distinguished by its usually homophyllous leaves, its perianth, which is enlarged at the base and constricted above the fruit, its longer perianth tube, and its yellow-green to tan, tubercled achenes.

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

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.)

Source FNA vol. 5, p. 551. FNA vol. 5, p. 565.
Parent taxa Polygonaceae > subfam. Polygonoideae > Polygonum > sect. Polygonum Polygonaceae > subfam. Polygonoideae > Polygonum > sect. Duravia
Sibling taxa
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. striatulum, P. tenue, P. utahense
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
Synonyms P. erectum subsp. achoreum
Name authority S. F. Blake: Rhodora 19: 232. (1917) S. Watson: Proc. Amer. Acad. Arts 14: 294. (1879)
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