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bushy knotweed, yellow knotweed, yellow-flower knotweed

pleat-leaf knotweed, slender 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 or brown-ish, simple or branched from below middle, not wiry, 5–50 cm, glabrous or 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 caducous or persistent, distal leaves abruptly reduced to bracts;

ocrea 6–15 mm, glabrous or papillose-scabridulous, proximal part cylindric, distal part soon disintegrating into a few brown fibers;

petiole 0.1–1 mm;

blade 1-veined, with 1 pleat on each side of midrib, narrowly lanceolate to linear, 25–40 × 1–8 mm, margins usually flat, papillose-denticulate, apex mucronate or cuspidate.

Inflorescences

axillary or axillary and terminal, spikelike;

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

axillary and terminal, spikelike, slender, elongate;

cymes spaced along branches, 1–2(–3)-flowered.

Pedicels

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

enclosed in ocreae, erect, 1–1.5 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).

closed;

perianth 2.5–4.2 mm;

tube 15–22% of perianth length;

tepals overlapping, green, often brownish when dried, with pink or white margins, petaloid or sepaloid, elliptic, cucullate, navicular, apex rounded;

midveins usually unbranched, rarely branched;

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 or slightly exserted from perianth, black, elliptic to oblong, 2.3–4 mm, faces subequal, shiny, smooth or minutely striate-tubercled near edges and apex.

2n

= 20.

Polygonum ramosissimum

Polygonum tenue

Phenology Flowering Jun–Oct.
Habitat Dry acid soils in exposed sites
Elevation 100-1000 m (300-3300 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
AL; AR; CT; DC; DE; GA; IA; IL; IN; KS; KY; LA; MA; MD; ME; MI; MN; MO; NC; NE; NH; NJ; NY; OH; OK; PA; RI; SD; TN; TX; VA; VT; WI; WV; WY; ON
[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. 567.
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. 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. utahense
Subordinate taxa
P. ramosissimum subsp. prolificum, P. ramosissimum subsp. ramosissimum
Synonyms P. tenue var. protrusum
Name authority Michaux: Fl. Bor.-Amer. 1: 237. (1803) Michaux: Fl. Bor.-Amer. 1: 238. (1803)
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