Stems ascending to erect or, rarely, prostrate, usually branched, sometimes simple, unarmed. Leaves: ocrea chartaceous, rarely foliaceous distally, margins eciliate or ciliate; petiole not winged, not auriculate; blade sometimes with dark triangular or lunate blotch adaxially, lanceolate to narrowly elliptic, base tapered, acute, rounded, or cordate, margins entire. Inflorescences terminal or terminal and axillary, spikelike, uninterrupted or interrupted. Flowers homostylous or heterostylous, articulation swollen or not; perianth campanulate; tepals 4–5, connate 1/4–2/3 their length; stamens 5–8; styles deciduous, 2–3, included or exserted (exserted syles and stamens in heterostylous species), spreading.

Distribution

Nearly worldwide, especially n temperate regions

Discussion

Species ca. 60 (16 in the flora).

Members of sect. Persicaria frequently grow in moist or inundated habitats. Many have evolved responses to submergence that allow them to survive extended periods of inundation (R. S. Mitchell 1976). Hybridization often is implicated for the taxonomic difficulties in the section. However, J. Timson (1965) concluded that, at least among annual European species, hybridization is rare due to autogamous breeding systems. Mitchell (1971) demonstrated the usefulness of leaf morphology in distinguishing major groups among the native North American smartweeds.

Selected References

Consaul, L. L., S. I. Warwick, and J. McNeill. 1991. Allozyme variation in the Polygonum lapathifolium complex. Canad. J. Bot. 69: 2261–2270.

Dalci, M. 1972. The Taxonomy of Section Persicaria (Tourn.) L. in the Genus Polygonum (Tourn.) L. (Polygonaceae) in the United States East of the Rocky Mountains. Ph.D. dissertation. University of Nebraska. Mc

Donald, C. B. 1980. A biosystematic study of the Polygonum hydropiperoides (Polygonaceae) complex. Amer. J. Bot. 67: 664–670.

Timson, J. 1963. The taxonomy of Polygonum lapathifolium L., P. nodosum Pers., and P. tomentosum Schrank. Watsonia 5: 386–395.

Yang, J. and Wang J. W. 1991. A taxometric analysis of characters of Polygonum lapathifolium L. Acta Phytotax. Sin. 29: 258–263.

Lower Taxa

Persicaria amphibia, Persicaria bicornis, Persicaria careyi, Persicaria glabra, Persicaria hirsuta, Persicaria hydropiper, Persicaria hydropiperoides, Persicaria lapathifolia, Persicaria longiseta, Persicaria maculosa, Persicaria minor, Persicaria orientalis, Persicaria pensylvanica, Persicaria punctata, Persicaria robustior, Persicaria setacea

Key

1	Some or all ocreae foliaceous and green distally	> 2
1	All ocreae chartaceous and hyaline, tan, brown, or reddish brown throughout, never foliaceous and green distally	> 3
2	Plants annual; rhizomes and stolons absent; leaf blades ovate, 3-17 cm wide	Persicaria orientalis
2	Plants perennial; rhizomes or stolons usually present; leaf blades ovate-lanceolate to elliptic or oblong-lanceolate, 1-6(-8) cm wide	Persicaria amphibia
3	Perianths glandular-punctate	> 4
3	Perianths not glandular-punctate	> 9
4	Achenes minutely roughened, dull; axillary inflorescences sometimes enclosed in ocreae	Persicaria hydropiper
4	Achenes smooth, shiny; inflorescences never enclosed in ocreae	> 5
5	Outer tepals with anchor-shaped veins; achenes discoid	Persicaria lapathifolia
5	Outer tepals without anchor-shaped veins; achenes 3-gonous or biconvex	> 6
6	Ocreae margins eciliate; achenes biconvex; styles 2	Persicaria glabra
6	Ocreae margins ciliate with bristles 2-12 mm; achenes usually 3-gonous, rarely biconvex; styles 2-3	> 7
7	Punctae confined to bases of perianths and sometimes on inner tepals	Persicaria hydropiperoides
7	Punctae ± uniformly distributed over perianths	> 8
8	Inflorescences interrupted; ocreolae mostly not overlapping, margins mostly ciliate with hairs to 2 mm; leaf blades 0.6-2.4 cm wide	Persicaria punctata
8	Inflorescences uninterrupted; ocreolae usually overlapping, margins mostly eciliate or proximal sometimes with hairs to 1 mm; leaf blades 2-4.5 cm wide	Persicaria robustior
9	Peduncles stipitate-glandular	> 10
9	Peduncles not stipitate-glandular	> 14
10	Plants perennial; rhizomes or stolons usually present; inflorescences terminal	Persicaria amphibia
10	Plants annual; rhizomes and stolons absent; inflorescences terminal and axillary	> 11
11	Stems hirsute proximally; margins of ocreae ciliate with bristles 2-7 mm	Persicaria careyi
11	Stems glabrous proximally; margins of ocreae eciliate or ciliate with bristles less than 1 mm	> 12
12	Outer tepals with anchor-shaped veins; tepals 4(-5); inflorescences mostly arching or nodding	Persicaria lapathifolia
12	Outer tepals without anchor-shaped veins; tepals 5; inflorescences erect or, rarely, nodding	> 13
13	Flowers homostylous; achenes without central hump on 1 side	Persicaria pensylvanica
13	Flowers heterostylous; achenes usually with central hump on 1 side	Persicaria bicornis
14	Plants perennial; rhizomes or stolons usually present	> 15
14	Plants annual; rhizomes and stolons absent	> 19
15	Achenes biconvex; styles 2	> 16
15	Achenes 3-gonous; styles 3	> 17
16	Perianth greenish white or white to pink; surfaces of ocreae glabrous, usually obscurely glandular-punctate	Persicaria glabra
16	Perianth roseate to red; surfaces of ocreae glabrous or appressed-pubescent to hirsute, not glandular-punctate	Persicaria amphibia
17	Proximal part of ocreae strigose, or ocreae glabrous	Persicaria hydropiperoides
17	Proximal part of ocreae hirsute, or strigose and with loosely ascending to spreading hairs at least proximally	> 18
18	Bases of leaf blades rounded to cordate; stems brownish-hirsute on internodes	Persicaria hirsuta
18	Bases of leaf blades tapered to truncate; stems glabrous or loosely appressed- to spreading-hirsute near nodes	Persicaria setacea
19	Margins of ocreae without bristles or with bristles to 1 mm; ocreolae mostly overlapping; achenes discoid, rarely 3-gonous	> 20
19	Margins of ocreae ciliate with bristles (0.2-)1-12 mm, if bristles less than 1 mm then ocreolae not overlapping; achenes discoid, biconvex, or 3-gonous	> 22
20	Outer tepals with anchor-shaped veins; tepals 4(-5); inflorescences mostly arching or nodding	Persicaria lapathifolia
20	Outer tepals without anchor-shaped veins; tepals 5; inflorescences mostly erect, rarely nodding	> 21
21	Flowers homostylous; achenes without central hump on 1 side	Persicaria pensylvanica
21	Flowers heterostylous; achenes usually with central hump on 1 side	Persicaria bicornis
22	Inflorescences not dense; ocreolae not overlapping proximally, usually overlapping distally; leaf blades linear to linear-lanceolate	Persicaria minor
22	Inflorescences dense; ocreolae mostly overlapping; leaf blades narrowly ovate or ovate-lanceolate to linear-lanceolate	> 23
23	Bristles of ocreolae 0.2-1.3(-2) mm; achenes discoid, biconvex, or 3-gonous; styles 2-3	Persicaria maculosa
23	Bristles of ocreolae (0.5-)1-4(-6) mm; achenes 3-gonous; styles 3	Persicaria longiseta

"/2" is not declared as a valid unit of measurement for this property.