Polygonum ramosissimum |
Polygonum sect. Polygonum |
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bushy knotweed, yellow knotweed, yellow-flower knotweed |
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Habit | Plants yellowish green or bluish green, (dark brown to black after drying in subsp. prolificum), heterophyllous or homophyllous. | Herbs, annual (perennial and rhizomatous in P. striatulum), not compact, not cushionlike, homophyllous or heterophyllous, frequently heterocarpic, rarely subsucculent (in P. marinense and P. fowleri). | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Stems | erect, usually profusely branched in distal 1/2, not wiry, 10–100(–200) cm. |
prostrate, decumbent, or ascending to erect, straight (zigzag in P. fowleri and P. humifusum), distinctly and ± regularly 8–16-ribbed, smooth (papillose-scabridulous in P. plebeium). |
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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. |
ocrea 4–12-veined (1-veined in P. plebeium), proximal part not pruinose (pruinose in P. glaucum and P. oxyspermum); petiole articulated to proximal part of ocrea, when absent, blade is directly articulated to ocrea; blade linear to elliptic or obovate, rarely coriaceous (in P. glaucum), smooth (papillose in P. plebeium, rugulose and glaucous in P. glaucum); venation pinnate, secondary veins conspicuous. |
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Inflorescences | axillary or axillary and terminal, spikelike; cymes uniformly distributed or crowded toward tips of branches, 2–5-flowered. |
usually axillary, less commonly axillary and terminal; cymes 1–7(–10)-flowered. |
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Pedicels | enclosed in or exserted from ocreae, 1–6 mm. |
erect to spreading, 0.5–7 mm. |
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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). |
usually closed, sometimes semi-open; tepals ± monomorphic, outer tepals equaling or somewhat larger than inner, apices of outer tepals rounded; anthers whitish yellow. |
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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. |
ovate to ovate-lanceolate, 2–3-gonous, shiny or dull, smooth to roughened or tubercled. |
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Polygonum ramosissimum |
Polygonum sect. Polygonum |
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Distribution |
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
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Nearly worldwide |
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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.) |
Species ca. 45 (13 in the flora). Plants of sect. Polygonum produce two types of fruits (heterocarpy). Summer achenes are brown, ovate, and tubercled to smooth; late-season (autumn) achenes are hypertrophied, olivaceous, two to five times as long as the summer achenes, lanceolate, and smooth. The two types differ in their germination biology. Late-season achenes possess a low, innate dormancy and can germinate immediately after being produced, at 20–25°C (O. V. Yurtseva et al. 1999). Lower temperatures will delay germination until the following spring. Summer achenes are dormant when produced and undergo a cyclical dormant/nondormant pattern in the soil (A. D. Courtney 1968; J. M. Baskin and C. C. Baskin 1990). Mature, early-season plants bearing leaves, flowers, and achenes are necessary for accurate determinations. Late-autumn specimens with hypertrophied achenes often are difficult or impossible to identify. In the descriptions, measurements of leaves, ocreae, and petioles are from the middle of the main stem. Leaf length includes the petiole. Heterophyllous taxa have cauline leaves at least three times as long as the branch leaves; homophyllous plants have stem and branch leaves about equal in size. Heterophylly is easily detected in most cases. However, some taxa show considerable variability in leaf morphology; identification should not rely on heterophylly alone. The character states “flowers closed” and “flowers semi-open” should be observed on herbarium specimens. Perianth description refers to the fruiting perianth measured from the pedicel joint to the apex of the tepals. Tepal descriptions refer to the outer three tepals (except for P. heterosepalum). Trigonous achenes have one face broader than the other two. Descriptions refer only to the two narrower faces, which can be subequal or distinctly unequal. Surface of achenes is best observed at magnifications of (or higher than) 100×. The achene surface may be: smooth, when no ornamentation is visible; roughened, when the tubercles are not discernible but the surface appears roughened; striate-tubercled, when conspicuous tubercles are oriented in rows; uniformly tubercled, when the tubercles are dense and rows difficult to distinguish; and obscurely tubercled, when the tubercles are weakly marked, inconspicuous, or restricted to a few (three to 15) rows on the central parts of faces. Late-season achenes in all species are hypertrophied, olivaceous, lanceolate, exserted, and smooth. They have little taxonomic significance. (Discussion copyrighted by Flora of North America; reprinted with permission.) |
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Key |
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Source | FNA vol. 5, p. 551. | FNA vol. 5, p. 548. | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Parent taxa | Polygonaceae > subfam. Polygonoideae > Polygonum > sect. Polygonum | Polygonaceae > subfam. Polygonoideae > Polygonum | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
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Name authority | Michaux: Fl. Bor.-Amer. 1: 237. (1803) | unknown | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
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