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.

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