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bushy knotweed, yellow knotweed, yellow-flower knotweed

Engelmann's 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 purplish brown, branched from base, not wiry, 4–30 cm, glabrous or minutely 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 persistent, distal leaves abruptly reduced to bracts;

ocrea 3–5 mm, papillose-scabridulous or glabrous, proximal part funnelform, distal part becoming lacerate with age;

petiole 0.1–2 mm;

blade 1-veined, not pleated, linear-oblanceolate, 10–20(–25) × 1–3(–4) mm, margins revolute, smooth, apex acute to mucronate.

Inflorescences

axillary or axillary and terminal, spikelike;

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

axillary and terminal, spikelike, loosely floriferous nearly to base, elongate;

cymes spaced along branches, (1–)2–4-flowered.

Pedicels

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

exserted from ocreae, reflexed, 1–3 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 1.5–2(–2.5) mm;

tube 18–26% of perianth length;

tepals initially overlapping and cucullate, later forced apart by developing achene, greenish or sometimes purple, with white margins, petaloid or sepaloid, oblong, ± flat or navicular, apex rounded;

midveins unbranched;

stamens 5–8.

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.

exserted from perianth, black, elliptic, 1.2–2.3 mm, faces subequal, shiny, smooth.

Polygonum ramosissimum

Polygonum engelmannii

Phenology Flowering Jun–Sep.
Habitat Dry to moist sandy or well-drained soils, sagebrush desert to lower mountains
Elevation 1000-1500 m (3300-4900 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
CO; ID; MT; NV; SD; UT; WY; AB; BC
[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. 569.
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. 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
Subordinate taxa
P. ramosissimum subsp. prolificum, P. ramosissimum subsp. ramosissimum
Synonyms P. douglasii subsp. engelmannii
Name authority Michaux: Fl. Bor.-Amer. 1: 237. (1803) Greene: Bull. Calif. Acad. Sci. 1: 126. (1885)
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