Polygonum nuttallii |
Polygonum striatulum |
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Nuttall's knotweed |
striped knotweed, Texas knotweed |
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Habit | Herbs. | Plants perennial, light green, heterophyllous; rhizomes brown, 0.7–3 cm diam. |
Stems | spreading to erect, sometimes zigzagged, purplish, simple or branched, wiry, (5–)10–35 cm, papillose-scabridulous. |
erect to ascending, sparingly branched in distal 1/2, not wiry, 25–60 cm. |
Leaves | evenly distributed or crowded at branch tips, articulated to ocreae, basal leaves persistent, distal leaves gradually reduced to bracts; ocrea 3–4 mm, papillose-scabridulous, proximal part funnelform, distal part finely lacerate; petiole 0.1–2 mm; blade 1-veined, not pleated, linear to narrowly oblong-elliptic, 8–30 × 1–4(–7) mm, margins narrowly revolute, never touching along midrib, smooth, apex acute, mucronate, ± glaucous adaxially. |
ocrea 6–12 mm, proximal part cylindric, distal part soon disintegrating into brown fibers, later leaving almost no fibrous remains; petiole 0–2 mm; blade light green, linear-lanceolate to oblanceolate, 8–35 × 2–8 mm, margins flat, apex acute or obtuse; stem leaves 2.1–4 times as long as adjacent branch leaves; distal leaves sharply reduced, not overtopping flowers (shorter than or equaling flowers). |
Inflorescences | axillary and terminal, spikelike, dense; cymes mostly congested toward tips of branches, 2–3-flowered. |
axillary and terminal, spikelike; cymes in distal nodes, 2–6-flowered. |
Pedicels | enclosed in ocreae, erect to spreading, 2–3 mm. |
exserted from ocreae, 2–4 mm. |
Flowers | semi-open or closed; perianth 1.8–2.4 mm; tube 25–33% of perianth length; tepals overlapping, greenish, white, or pink with pink margins, petaloid, oblong, cucullate, navicular in distal 1/4, apex rounded; midveins unbranched; stamens 8. |
semi-open; perianth 2–3.5 mm; tube 18–25% of perianth length; tepals overlapping, green with white or sometimes pink margins, petaloid, not keeled, oblong to obovate, cucullate; midveins usually unbranched; stamens 7–8. |
Achenes | enclosed in perianth, black, elliptic to ovate, 1.8–2.3 mm, faces subequal, shiny, smooth. |
enclosed in perianth, brown, ovate, 3-gonous, (1.6–)1.8–2.6(–3) mm, faces subequal or unequal, apex not beaked, edges concave, shiny, smooth or roughened; late-season achenes common, 4–6 mm. |
Polygonum nuttallii |
Polygonum striatulum |
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Phenology | Flowering May–Oct. | Flowering Dec–Mar or Jun–Oct. |
Habitat | Dry prairies, open knolls in lower mountains, open sites in lowland and montane zones, sandy soil | Seasonal moist places, sterile prairies, granitic soils |
Elevation | 800-1100 m (2600-3600 ft) | 100-700 m (300-2300 ft) |
Distribution |
OR; WA; BC
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TX |
Discussion | C. L. Hitchcock (1964) suggested that Polygonum nuttallii is but a small-flowered form of P. spergulariiforme. Although morphologically similar, P. nuttallii differs from P. spergulariiforme in some respects, including its wiry, purplish stems, short and funnelform ocreae, adaxially glaucous leaves, longer bracts, shorter fruiting perianth, and achenes. (Discussion copyrighted by Flora of North America; reprinted with permission.) |
Plants with leaves less-conspicuously veined, flowering August to October, and growing in seasonally moist habitats in central and western Texas are recognized by some authors as Polygonum texense or P. striatulum var. texense (M. Costea and F. J. Tardif 2003). (Discussion copyrighted by Flora of North America; reprinted with permission.) |
Source | FNA vol. 5, p. 570. | FNA vol. 5, p. 550. |
Parent taxa | Polygonaceae > subfam. Polygonoideae > Polygonum > sect. Duravia | Polygonaceae > subfam. Polygonoideae > Polygonum > sect. Polygonum |
Sibling taxa | ||
Synonyms | P. intermedium, P. douglasii subsp. nuttallii | P. striatulum var. texense, P. texense |
Name authority | Small: Mongr. Amer. Sp. Polygonum, 132, plate 53. (1895) | B. L. Robinson: Proc. Boston Soc. Nat. Hist. 31: 263. (1904) |
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