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common smartweed, marsh-pepper smartweed, marshpepper knotweed, mild water-pepper, renouée poivre-d'eau, smartweed, water-pepper, water-pepper smartweed

garden knotweed, garden smartweed, Himalayan knotweed, Kashmir plume

Habit Plants annual, 2–8(–10) dm; roots also often arising from proximal nodes; rhizomes and stolons absent.
Stems

decumbent to ascending or erect, branched, without noticeable ribs, glabrous, glandular-punctate.

Leaves

ocrea brown, cylindric or funnelform, (8–)10–15 mm, chartaceous, base inflated, margins truncate, ciliate with bristles 1–4 mm, surface glabrous or strigose, usually glandular-punctate;

petiole 0.1–0.8 cm, glandular-punctate, leaves sometimes sessile;

blade without dark triangular or lunate blotch adaxially, lanceolate to narrowly rhombic, (1.5–)4–10(–15) × 0.4–2.5 cm, base tapered or cuneate, margins antrorsely strigose, apex acute to acuminate, faces glabrous or scabrous along midveins, glandular-punctate, sometimes obscurely so adaxially.

Inflorescences

terminal and axillary, erect or nodding, interrupted or uninterrupted distally, 30–180 × 5–9 mm;

peduncle (0–)10–50 mm, sometimes absent on axillary inflorescences and flowers thus enclosed in ocreae, glabrous, glandular-punctate;

ocreolae not overlapping or overlapping distally, margins eciliate or ciliate with bristles to 1 mm.

Pedicels

ascending, 1–3 mm.

Flowers

1–3(–5) per ocreate fascicle, homostylous;

perianth greenish proximally, white or pink distally, glandular-punctate with punctae ± uniformly distributed, scarcely accrescent;

tepals 4–5, connate ca. 1/3 their length, petaloid, obovate, 2–3.5 mm, veins prominent or not, not anchor-shaped, margins entire, apex obtuse to rounded;

stamens 6–8, included;

anthers pink or red, elliptic to ovate;

styles 2–3, connate proximally.

Achenes

included or apex exserted, brownish black, biconvex or 3-gonous, 1.9–3 × 1.5–2 mm, dull, minutely roughened.

2n

= 20.

Persicaria hydropiper

Persicaria wallichii

Phenology Flowering May–Nov.
Habitat Shorelines of lake and ponds, banks of streams and rivers, fens, forested wetlands, pastures, occasionally waste ground
Elevation 0-1500 m (0-4900 ft)
Distribution
from FNA
AK; AL; AR; CA; CO; CT; DC; DE; FL; 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; BC; MB; NB; NF; NS; ON; PE; QC; SPM; Europe; nw Africa; Pacific Islands (Hawaii, New Zealand); Australia [Introduced in North America; introduced also in Asia]
[WildflowerSearch map]
[BONAP county map]
from FNA
CA; MA; OR; BC; Asia
[WildflowerSearch map]
[BONAP county map]
Discussion

All parts of Persicaria hydropiper have an acrid, pepperlike taste. The plants have a long history of medicinal use in Europe, and the oily exudate produced in multicellular glands can cause skin irritation, hence the common name smartweed (R. S. Mitchell and J. K. Dean 1978). Some Native American tribes used P. hydropiper as a drug to treat a variety of ailments, and the Cherokee and Iroquois consumed it as food (D. E. Moerman 1998).

Herbarium specimens of Persicaria hydropiper often are misidentified as P. punctata. In addition to its minutely roughened and dull achenes, P. hydropiper differs from P. punctata frequently in bearing flowers enclosed in the ocreae, the inflorescences thus appearing somewhat leafy. By contrast, inflorescences of P. punctata generally appear terminal and leafless.

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

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.)

Source FNA vol. 5, p. 590. FNA vol. 5, p. 581.
Parent taxa Polygonaceae > subfam. Polygonoideae > Persicaria > sect. Persicaria Polygonaceae > subfam. Polygonoideae > Persicaria > sect. Rubrivena
Sibling taxa
P. amphibia, P. arifolia, P. bicornis, P. bungeana, P. capitata, P. careyi, P. chinensis, P. glabra, P. hirsuta, 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. wallichii
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
Subordinate taxa
P. wallichii var. wallichii
Synonyms Polygonum hydropiper, Polygonum hydropiper var. projectum Polygonum polystachyum, Aconogonon polystachyum, Pleuropteropyrum polystachyum, Reynoutria polystachya, Rubrivena polystachya
Name authority (Linnaeus) Spach: Hist. Nat. Vég. 10: 536. (1841) Greuter & Burdet: Willdenowia 19: 41. (1989)
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