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Himalayan smartweed, Japanese knotweed, pink bubble persicaria, pink-head knotweed, pink-head persicaria, pinkhead smartweed

knotweed, smartweed, tearthumb

Habit Plants annual or perennial, 0.5–5 dm; roots also often arising from proximal nodes. Herbs, perennial or annual (sometimes suffrutescent in P. wallichii); taprooted or fibrous-rooted; sometimes rhizomatous or stoloniferous.

prostrate, glabrous or glandular-pubescent.

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


ocrea brown or reddish brown, cylindric to funnelform, 5–12 mm, chartaceous, base inflated or not, margins oblique, eciliate or ciliate with bristles to 1.5 mm, surface lanate, sometimes also glandular-pubescent;

petiole 2–5 mm, winged distally;

blade ovate to elliptic, 1.5–4(–6) × 0.6–2.5(–3.3) cm, base cuneate or tapering, margins ciliate with reddish, multicellular hairs, apex acute, faces glandular-pubescent abaxially and adaxially, not glandular-punctate.

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.


terminal, 5–20 × 7-18 mm;

peduncle 10–40 mm, glabrous or stipitate-glandular in distal 1/5;

ocreolae overlapping, margins eciliate.

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

peduncle present.


spreading, 0.5–1 mm.

present or absent.


1–5 per ocreate fascicle;

perianth greenish white proximally, pinkish distally, urceolate, glabrous, nonaccrescent;

tepals 5, elliptic, 2–3 mm, apex acute to obtuse;

stamens 8, filaments distinct, free;

anthers pink to red, elliptic;

styles 3, connate to middle or distally.

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.


included, reddish brown to brownish black, 3-gonous, 1.5–2.2 × 1–1.5 mm, shiny, smooth or minutely punctate.

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


embryo curved.


= 10, 11, 12.

Persicaria capitata


Phenology Flowering Jun–Sep.
Habitat Disturbed, urban places
Elevation 0-500 m (0-1600 ft)
from FNA
CA; LA; OR; Asia (Bhutan, w China, n India, Nepal) [Introduced in North America; introduced also in the Pacific Islands (Hawaii)]
[WildflowerSearch map]
[BONAP county map]
Nearly worldwide
[BONAP county map]

Persicaria capitata is planted as a garden groundcover. It escapes infrequently in the flora area; once established outside of cultivation it can be difficult to eradicate.

(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 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. 579. FNA vol. 5, p. 574. Authors: Harold R. Hinds†, Craig C. Freeman.
Parent taxa Polygonaceae > subfam. Polygonoideae > Persicaria > sect. Cephalophilon Polygonaceae > subfam. Polygonoideae
Sibling taxa
P. amphibia, P. arifolia, P. bicornis, P. bungeana, 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. wallichii
Subordinate taxa
P. sect. Cephalophilon, P. sect. Echinocaulon, P. sect. Persicaria, P. sect. Rubrivena, P. sect. Tovara
Synonyms Polygonum capitatum Polygonum unranked P.
Name authority (Buchanan-Hamilton ex D. Don) H. Gross: Bot. Jahrb. Syst. 49: 277. (1913) (Linnaeus) Miller: Gard. Dict. Abr. ed. 4, vol. 3. (1754)
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