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

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

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

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.

Inflorescences

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

Pedicels

enclosed in ocreae, 1.3–1.8(–2) mm.

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.

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.

2n

= 40, 60.

Polygonum achoreum

Phenology Flowering Jul–Sep.
Habitat Disturbed areas, roadsides, sidewalks, edges of cultivated fields
Elevation 10-800 m (0-2600 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
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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.)

Source FNA vol. 5, p. 551.
Parent taxa Polygonaceae > subfam. Polygonoideae > Polygonum > sect. Polygonum
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
Synonyms P. erectum subsp. achoreum
Name authority S. F. Blake: Rhodora 19: 232. (1917)
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