Flora of North America species comparison

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Persicaria wallichii

Persicaria setacea

garden knotweed, garden smartweed, Himalayan knotweed, Kashmir plume

bog smartweed, bristly smartweed
Habit Plants perennial, 5–15 dm; roots also often arising from proximal nodes; rhizomes present, stolons sometimes produced on plants in water.
Stems

ascending or erect, branched distally, slightly ribbed, glabrous or loosely appressed- to spreading-hirsute near nodes.
Leaves

ocrea brown, cylindric, 10–20 mm, chartaceous, base usually inflated, margins truncate, ciliate with bristles 6–12 mm, surface strigose and with loosely ascending to spreading hairs at least proximally, not glandular-punctate;

petiole 0.1–0.5 cm, spreading-hirsute, leaves sometimes sessile;

blade without dark triangular or lunate blotch adaxially, lanceolate, (3–)6–15(–18) × (1.5–)2–3.2(–4.8) cm, base tapered to truncate, margins appressed-ciliate, apex acute to acuminate, faces sparsely hirsute to loosely appressed hirsute abaxially and adaxially.
Inflorescences

mostly terminal, erect, uninterrupted, 20–80 × 4–8 mm;

peduncle 10–70 mm, strigose;

ocreolae overlapping, margins ciliate with bristles (0.6–)1–3(–5) mm.
Pedicels

ascending, 1–3 mm.
Flowers

(1–)2–4(–5) per ocreate fascicle, homostylous;

perianth greenish proximally, creamy or tan distally, occasionally tinged pink, glabrous, not glandular-punctate, nonaccrescent;

tepals 5, connate ca. 1/3 their length, obovate, 2–3 mm, veins not prominent, not anchor-shaped, margins entire, apex obtuse to rounded;

stamens 5, included;

anthers pink or red, elliptic;

styles 3, connate proximally.
Achenes

included or apex exserted, brown to black, 3-gonous, (1.5–)2–2.5 × 1.2–1.7 mm, shiny, smooth.
2n

= 20.

Persicaria wallichii

Persicaria setacea
Phenology Flowering Jul–Oct.
Habitat Alluvial woods, swamp forests
Elevation 0-300 m (0-1000 ft)
Distribution
from FNA
CA; MA; OR; BC; Asia
[WildflowerSearch map]
[BONAP county map]
from FNA
AL; AR; DE; FL; GA; IL; IN; KY; LA; MA; MD; MI; MO; MS; NC; NJ; NY; OH; OK; PA; RI; SC; TN; TX; VA; WA
[WildflowerSearch map]
[BONAP county map]
Discussion

Varieties 2 (1 in the flora).

Persicaria wallichii is an ornamental that escapes infrequently in the flora area. A population in Nova Scotia apparently was ephemeral. Plants with leaf blades sparsely to densely pubescent abaxially and pedicels glabrous are var. wallichii, to which naturalized North American plants appear to be referable. Plants with leaf blades brownish-tomentose abaxially and pedicels usually pubescent are var. tomentosa S. P. Hong, which may be in cultivation in North America.

(Discussion copyrighted by Flora of North America; reprinted with permission.)

C. B. McDonald (1980) showed that Persicaria setacea is closely related to P. hirsuta and P. hydropiperoides. Hybrids between P. setacea and P. hirsuta have been produced experimentally but appear to be rare in the wild. Persicaria setacea and P. hydropiperoides occasionally occur in mixed populations but do not hybridize (McDonald). Persicaria setacea sometimes intergrades morphologically with P. hydropiperoides, especially in New England. Specimens of P. setacea without the characteristic ascending or spreading hairs on the ocreae usually can be distinguished from P. hydropiperoides by the extent of adnation of the hairs to the ocreae—up to one-third their lengths in P. setacea, but one-third to two-thirds their lengths in P. hydropiperoides.

(Discussion copyrighted by Flora of North America; reprinted with permission.)
Source FNA vol. 5, p. 581. FNA vol. 5, p. 588.
Parent taxa Polygonaceae > subfam. Polygonoideae > Persicaria > sect. Rubrivena Polygonaceae > subfam. Polygonoideae > Persicaria > sect. Persicaria
Sibling taxa
P. amphibia, P. arifolia, P. bicornis, P. bungeana, P. capitata, P. careyi, P. chinensis, P. glabra, P. hirsuta, P. hydropiper, P. hydropiperoides, P. lapathifolia, P. longiseta, P. maculosa, P. meisneriana, P. minor, P. nepalensis, P. orientalis, P. pensylvanica, P. perfoliata, P. punctata, P. robustior, P. sagittata, P. setacea, P. virginiana
P. amphibia, P. arifolia, P. bicornis, P. bungeana, P. capitata, P. careyi, P. chinensis, P. glabra, P. hirsuta, P. hydropiper, P. hydropiperoides, P. lapathifolia, P. longiseta, P. maculosa, P. meisneriana, P. minor, P. nepalensis, P. orientalis, P. pensylvanica, P. perfoliata, P. punctata, P. robustior, P. sagittata, P. virginiana, P. wallichii
Subordinate taxa
P. wallichii var. wallichii
Synonyms Polygonum polystachyum, Aconogonon polystachyum, Pleuropteropyrum polystachyum, Reynoutria polystachya, Rubrivena polystachya Polygonum setaceum, Polygonum hydropiperoides var. setaceum, Polygonum setaceum var. interjectum, Polygonum setaceum var. tonsum
Name authority Greuter & Burdet: Willdenowia 19: 41. (1989) (Baldwin) Small: Fl. S.E. U.S., 379. (1903)
Web links 
Unless otherwise noted, all data comes from the online version of the Flora of North America, who have made most of their content available via a Creative Commons license (CC BY 4.0).



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