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Asian knotweed, petite renouée, pygmy smartweed, small smartweed, small water-pepper

Nepalese knotweed, Nepalese smartweed

Habit Plants annual, 0.5–3(–4) dm; roots also sometimes at from proximal nodes; rhizomes and stolons absent. Plants annual, 3–5 dm; roots also often arising from proximal nodes.
Stems

decumbent or ascending, branched proximally, scarcely ribbed, glabrous or scabrous distally.

decumbent to ascending, glabrous except for fleshy, retrorse, whitish hairs at nodes.

Leaves

ocrea brownish, cylindric, 3–10 mm, chartaceous, base not inflated, margins truncate, ciliate with bristles (0.3–)1–3(–5) mm, surface glabrous or strigose, not glandular-punctate;

petiole 0.1–0.2 cm, glabrous or strigose, leaves sometimes sessile;

blade without dark triangular or lunate blotch adaxially, linear to linear-lanceolate, (1–)2–7.5(–10) × (0.2–)0.4–1(–2.3) cm, base tapered to cuneate, margins antrorsely scabrous, apex acute to acuminate, faces glabrous or sparingly strigose, especially along midveins, not glandular-punctate.

ocrea brownish or hyaline, cylindric to funnelform, 4–10 mm, chartaceous, base inflated or not, margins oblique, eciliate, surface glabrous or with bristlelike hairs proximally;

petiole 0.1–3 cm, winged to base, leaves sometimes sessile;

blade ovate-deltate, 1.5–5 × 1–4 cm, base rounded to truncate, margins glabrous or scabrous, apex acute, faces pilose and glandular-punctate abaxially, glabrous adaxially.

Inflorescences

terminal and axillary, ascending to erect, usually interrupted proximally, uninterrupted distally, 10–50 × 2–4 mm;

peduncle (0–)2–25 mm, sometimes absent on axillary inflorescences and flowers thus enclosed in ocreae, glabrous;

ocreolae not overlapping proximally, usually overlapping distally, margins ciliate with bristles (0.1–)0.6–2(–2.7) mm.

terminal and axillary, 5–10 × 5–10 mm;

peduncle 2–20 mm, apex stipitate-glandular;

ocreolae overlapping, margins eciliate.

Pedicels

ascending, 0.5–1 mm.

mostly ascending, 0.1–1 mm, flowers sometimes sessile.

Flowers

1–3(–4) per ocreate fascicle, homostylous;

perianth roseate to red, rarely white, glabrous, not glandular-punctate, scarcely accrescent;

tepals 5, connate ca. 1/3 their length, obovate to elliptic, 2.5–3 mm, veins not prominent, not anchor-shaped, margins entire, apex obtuse to rounded;

stamens 5(–6), included;

anthers yellow to pink, elliptic;

styles 2(–3), connate at bases.

1–2 per ocreate fascicle;

perianth white to pink or lavender, urceolate, glabrous, scarcely accrescent;

tepals 4(–5), oblong to broadly elliptic, 2.5–3 mm, apex acute to obtuse;

stamens (5–)8, filaments distinct, free;

anthers purplish black, elliptic;

styles 2, connate proximally.

Achenes

included, brownish black to black, biconvex or, rarely, 3-gonous, (1.5–)1.8–2.3(– 2.7) × (1.1–)1.3–1.5(–1.8) mm, shiny, smooth.

included, dark brown to black, biconvex, 1.5–2 × 1–1.5 mm, dull, minutely punctate.

Persicaria minor

Persicaria nepalensis

Phenology Flowering Jul–Oct. Flowering Jul–Oct.
Habitat Damp, open places Disturbed sites, gravel bars in lowland zone
Elevation 0-100 m (0-300 ft) 0-900 m (0-3000 ft)
Distribution
from FNA
CT; IN; LA; MA; NE; PA; VA; VT; NB; ON; QC; Europe [Introduced in North America]
[WildflowerSearch map]
[BONAP county map]
from FNA
CT; FL; MA; NY; PA; BC; Asia [Introduced in North America; introduced also in Europe, Africa]
[BONAP county map]
Discussion

Persicaria minor is synonymized with P. maculosa in most North American floras; its distribution in the flora area is poorly known. Hybrids between P. minor and P. maculosa have been documented in Europe (R. H. Roberts 1977).

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

Source FNA vol. 5, p. 593. FNA vol. 5, p. 579.
Parent taxa Polygonaceae > subfam. Polygonoideae > Persicaria > sect. Persicaria Polygonaceae > subfam. Polygonoideae > Persicaria > sect. Cephalophilon
Sibling taxa
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. 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. orientalis, P. pensylvanica, P. perfoliata, P. punctata, P. robustior, P. sagittata, P. setacea, P. virginiana, P. wallichii
Synonyms Polygonum minus, Polygonum minus var. subcontinuum Polygonum nepalense
Name authority (Hudson) Opiz: Seznam, 72. (1852) (Meisner) H. Gross: Bot. Jahrb. Syst. 49: 277. (1913)
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