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amphibious bistort, r enouée amphibie, water knotweed, water smartweed

arrow-leaf knotweed, arrow-leaf tearthumb, arrow-vine, renouée sagittée

Habit Plants perennial, 2–12 dm in terrestrial plants, to 30 dm in some aquatic plants; roots also sometimes arising from proximal nodes; rhizomes or stolons usually present. Plants annual, 3–20 dm; roots also often arising from proximal nodes.
Stems

prostrate to ascending or erect, simple or branched, ribbed, glabrous or strigose to hirsute.

scandent, ribbed, glabrous;

prickles 1–1.5 mm.

Leaves

ocrea tan to dark brown, cylindric or flared distally, 5–50 mm, chartaceous or, sometimes, foliaceous distally, base inflated, margins truncate to oblique, glabrous or ciliate with hairs 0.5–4.5 mm, surface glabrous or appressed-pubescent to hirsute, not glandular-punctate;

petiole 0.1–3(–7) cm, glabrous or appressed-pubescent to hirsute, leaves sometimes sessile;

blade without dark triangular or lunate blotch adaxially, ovate-lanceolate to elliptic or oblong-lanceolate, 2–15(–23) × 1–6(–8) cm, base usually tapered to acute or rounded, rarely cordate, margins antrorsely scabrous, apex acute to acuminate, faces glabrous or sparingly strigose, midveins glabrous or strigose, not glandular-punctate.

ocrea brownish, cylindric, (3–)5–13 mm, chartaceous, base inflated or not, without prickles, margins oblique, glabrous or ciliate at tip with bristles 0.2–1 mm, surface glabrous;

petiole 0.5–4 cm;

blade broadly lanceolate to oblong, 2–8.5 × 1–3 cm, base sagittate to cordate, margins entire, ciliate or eciliate, apex obtuse to acute, faces glabrous or densely appressed-pubescent, usually with retrorse prickles along midvein abaxially.

Inflorescences

terminal, ascending to erect, uninterrupted or interrupted proximally, 10–150 × 8–20 mm;

peduncle 10–50 mm, glabrous or strigose to hirsute, often stipitate-glandular;

ocreolae overlapping except sometimes proximal ones, margins ciliate with bristles to 1 mm.

capitate or paniclelike, uninterrupted, 5–15 × 4–10 mm;

peduncle 10–80 mm, usually glabrous, sometimes with retrorse prickles proximally;

ocreolae overlapping, margins eciliate.

Pedicels

ascending, 0.5–1.5 mm.

mostly ascending, 1–1.5 mm.

Flowers

bisexual or functionally unisexual, some plants having only staminate flowers, others with only pistillate flowers, 1–3(–4) per ocreate fascicle, heterostylous;

perianth roseate to red, glabrous, not glandular-punctate, slightly accrescent;

tepals 5, connate ca. 1/3 their lengths, obovate to elliptic, 4–6 mm, veins prominent, not anchor-shaped, margins entire, apex rounded to acute;

stamens 5, included or exserted;

anthers pink or red, elliptic;

styles 2, included or exserted, connate 1/2–2/3 their length.

2–3 per ocreate fascicle;

perianth white or greenish white, often tinged pink or red, sometimes entirely pink, glabrous, accrescent, not becoming blue and fleshy in fruit;

tepals 5, connate 1/3–1/2 their length, broadly elliptic, 3–5 mm, apex obtuse;

stamens 8, filaments distinct, free;

anthers pink, ovate;

styles 3, connate to middle.

Achenes

included, dark brown, biconvex, (2–)2.2–3 × (1.5–)1.8–2.6 mm, shiny or dull, smooth or minutely granular.

included or styles exserted, light or dark brown to black, 3-gonous, 2.5–4 × 1.8–2.5 mm, dull to shiny, smooth to minutely punctate.

2n

= 66, 132.

= 40.

Persicaria amphibia

Persicaria sagittata

Phenology Flowering Jun–Sep. Flowering Jun–Oct.
Habitat Shallow water, shorelines of ponds and lakes, banks of rivers and streams, moist prairies and meadows Moist shaded sites, meadows, pastures, fens, swamps, shorelines of ponds and streams
Elevation 0-3000 m (0-9800 ft) 0-1000 m (0-3300 ft)
Distribution
from FNA
AK; AR; AZ; CA; CO; CT; DC; DE; 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; AB; BC; MB; NB; NL; NS; NT; PE; QC; SK; YT; SPM; Mexico; South America; Ont ; Eurasia; Africa
[WildflowerSearch map]
[BONAP county map]
from FNA
AL; AR; CO; CT; DC; DE; FL; GA; IA; IL; IN; KS; KY; LA; MA; MD; ME; MI; MN; MO; MS; NC; ND; NE; NH; NJ; NY; OH; OK; PA; RI; SC; SD; TN; TX; VA; VT; WI; WV; MB; NB; NF; NS; ON; PE; QC; e Asia
[WildflowerSearch map]
[BONAP county map]
Discussion

Persicaria amphibia is widespread in the Northern Hemisphere and naturalized in Mexico, South America, and southern Africa. It is highly polymorphic and the most hydrophytic of the native North American smartweeds (R. S. Mitchell 1976). In recent decades, botanists have tended to follow Mitchell (1968) in recognizing two endemic, intergrading North American varieties. Studies by G. Turesson (1961) and Mitchell (1968, 1976) have shown that phenotypic extremes in the species are part of a cline of nearly continuous morphological variation that is strongly correlated with submergence, but also with some genetic integrity. Formal recognition of varieties is even less tenable when Eurasian elements also are considered.

Aquatic-adapted plants, which bloom in water or are sometimes stranded on land, have been called var. stipulacea (although that epithet may not be the oldest one available for the taxon). They produce ovoid-conic to short-cylindric inflorescences 10–40(–60) mm, prostrate aerial stems, and leaf blades that are glabrous with acute to rounded apices. Terrestrial forms of this ecotype usually are spreading-pubescent and often bear ocreae that are foliaceous, green, and flared distally, characters found only in North American plants (R. S. Mitchell 1968).

Terrestrial-adapted plants, referred to var. emersa, bloom on moist soil and produce short- to elongate-cylindric inflorescences 40–110(–150) mm, spreading or erect aerial stems, and leaf blades that are appressed-pubescent with acute to acuminate apices. They produce ocreae that are entirely chartaceous and not flared distally. Emergent and terrestrial plants of this ecotype exhibit less phenotypic plasticity and a lower frequency of heterostyly than do plants of the aquatic ecotype (R. S. Mitchell 1968).

R. S. Mitchell and J. K. Dean (1978) and H. R. Hinds (2000) recognized var. amphibia, the Eurasian element, as introduced in New York and New Brunswick, respectively. These plants are morphologically intermediate between the North American ecotypes and often indistinguishable from North American plants (Mitchell and Dean).

The Meskwaki and Ojibwa used leaves, stems, and roots as a drug to treat a variety of maladies, the Potawatomi used roots to treat unspecified ailments, and the Lakota and Sioux used plants for food (D. E. Moerman 1998).

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

Persicaria sagittata is an extremely variable species. Achene and leaf characters have been used by some authors to separate North American and Asian populations, but these characters show weak geographic variation (C. W. Park 1988).

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

Source FNA vol. 5, p. 583. FNA vol. 5, p. 577.
Parent taxa Polygonaceae > subfam. Polygonoideae > Persicaria > sect. Persicaria Polygonaceae > subfam. Polygonoideae > Persicaria > sect. Echinocaulon
Sibling taxa
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, 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. setacea, P. virginiana, P. wallichii
Synonyms Polygonum amphibium, P. amphibia var. emersa, P. amphibia var. stipulacea, P. coccinea, P. hartwrightii, P. muhlenbergia, Polygonum amphibium var. emersum, Polygonum amphibium subsp. laevimarginatum, Polygonum amphibium var. natans, Polygonum amphibium var. stipulaceum, Polygonum coccineum, Polygonum coccineum var. pratincola, Polygonum coccineum var. rigidulum, Polygonum emersum, Polygonum hartwrightii, Polygonum natans Polygonum sagittatum, Polygonum sagittatum var. gracilentum, Tracaulon sagittatum, Truellum sagittatum
Name authority (Linnaeus) Gray: Nat. Arr. Brit. Pl. 2: 268. (1822) (Linnaeus) H. Gross: Beih. Bot. Centralbl. 37(2): 113. (1919)
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