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

knotweed, smartweed, tearthumb

Habit Plants annual, 2–8(–10) dm; roots also often arising from proximal nodes; rhizomes and stolons absent. Herbs, perennial or annual (sometimes suffrutescent in P. wallichii); taprooted or fibrous-rooted; sometimes rhizomatous or stoloniferous.
Stems

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

erect or, sometimes, prostrate or scandent, simple or branched, glabrous or pubescent, rarely with recurved prickles.

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.

deciduous, mostly cauline, alternate, petiolate or sessile;

ocrea persistent or disintegrating with age and deciduous entirely or distally, usually tan, brown, or reddish, chartaceous or partially to entirely foliaceous, rarely coriaceous proximally and chartaceous distally, glabrous or scabrous to variously pubescent, never 2-lobed distally;

blade lanceolate or ovate to hastate or sagittate, margins entire or, rarely, hastately lobed.

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.

terminal or terminal and axillary, spikelike, paniclelike, or capitate;

peduncle present.

Pedicels

ascending, 1–3 mm.

present or absent.

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.

bisexual (often functionally unisexual in P. amphibia and P. hydropiperoides), 1–14 per ocreate fascicle, base not stipelike;

perianth white, greenish white, roseate, red, or purple, campanulate or urceolate, rarely rotate, rarely becoming fleshy in fruit, glabrous, sometimes glandular-punctate, accrescent or nonaccrescent;

tepals 4–5, connate 1/4–2/3 their lengths (less than 1/5 their lengths in P. wallichii), petaloid, dimorphic, outer larger than inner;

stamens 5–8, filaments distinct or connate basally, outer ones sometimes adnate to perianth tube, glabrous;

anthers yellow, pink, or red, elliptic to ovate;

styles 2–3, erect to spreading or reflexed, distinct or connate;

stigmas capitate.

Achenes

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

included or exserted, brown or dark brown to black, not winged, discoid, biconvex, 2–3-gonous, or spheroidal, glabrous.

Seeds

embryo curved.

x

= 10, 11, 12.

2n

= 20.

Persicaria hydropiper

Persicaria

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]
Nearly worldwide
[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.)

Species ca. 100 (26 in the flora).

Opinions vary widely about the circumscription and infrageneric classification of Persicaria. The concept employed here generally follows L.-P. Ronse Decraene et al. (2000) and K. Haraldson (1978), with five sections recognized in the flora. Aconogonon and Bistorta, which often are included in Persicaria or in Polygonum in the broad sense, are treated here as separate genera.

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

Key

Key to the Sections of Persicaria

1. Styles exserted, persistent on achenes; inflorescences spikelike, interrupted
sect. Tovara
1. Styles included, rarely exserted, deciduous; inflorescences capitate, paniclelike, or spikelike, uninterrupted or interrupted
→ 2
2. Stems with recurved prickles, scandent or, rarely, ascending to erect
sect. Echinocaulon
2. Stems unarmed, usually erect or ascending, rarely prostrate or decumbent
→ 3
3. Inflorescences capitate; petioles usually winged, auriculate
sect. Cephalophilon
3. Inflorescence spikelike or paniclelike; petioles not winged, not auriculate
→ 4
4. Inflorescences paniclelike; perianths rotate; tepals connate less than 1/ 5 their lengths
sect. Rubrivena
4. Inflorescences spikelike; perianths campanulate; tepals connate 1/ 2/ 3 their lengths
sect. Persicaria
Source FNA vol. 5, p. 590. FNA vol. 5, p. 574. Authors: Harold R. Hinds†, Craig C. Freeman.
Parent taxa Polygonaceae > subfam. Polygonoideae > Persicaria > sect. Persicaria Polygonaceae > subfam. Polygonoideae
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
Subordinate taxa
P. sect. Cephalophilon, P. sect. Echinocaulon, P. sect. Persicaria, P. sect. Rubrivena, P. sect. Tovara
Synonyms Polygonum hydropiper, Polygonum hydropiper var. projectum Polygonum unranked P.
Name authority (Linnaeus) Spach: Hist. Nat. Vég. 10: 536. (1841) (Linnaeus) Miller: Gard. Dict. Abr. ed. 4, vol. 3. (1754)
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