Bristly Lady's Thumb

Persicaria longiseta is morphologically similar to another Asian species, P. posumbu (Buchanan-Hamilton ex D. Don) H. Gross (= P. caespitosa). Its spread in the United States since its introduction near Philadelphia in 1910 was summarized by A. K. Paterson (2000).

Plants annual, 3-8 dm; roots also often arising from proximal nodes; rhizomes and stolons absent. Stems decumbent to ascending, branched, without noticeable ribs, glabrous. Leaves: ocrea hyaline to brownish, cylindric, 5-12 mm, chartaceous, base sometimes inflated, margins truncate, ciliate with bristles 4-12 mm, surface glabrous or strigose, not glandular-punctate; petiole 0.1-0.3(-0.6) cm, glabrous, leaves sometimes sessile; blade without dark triangular or lunate blotch adaxially, ovate-lanceolate to linear-lanceolate, 2-8 × 1-3 cm, base tapering to cuneate, margins antrorsely strigose, apex acute to acuminate, faces glabrous or sparingly strigose along veins abaxially, glabrous or strigose along midvein and margins adaxially, not glandular-punctate. Inflorescences terminal, sometimes also axillary, erect, uninterrupted, 10-40(-80) × 3-7 mm; peduncle 10-50 mm, glabrous; ocreolae overlapping, margins ciliate with bristles (0.5-)1-4(-6) mm. Pedicels ascending, 1-2 mm. Flowers 1-5 per ocreate fascicle, homostylous; perianth pinkish green proximally, roseate distally, glabrous, not glandular-punctate, scarcely accrescent; tepals 5, connate ca. 1/ 3 their length, obovate, 2.2-2.8 mm, veins not prominent, not anchor-shaped, margins entire, apex obtuse to rounded; stamens 5, included; anthers yellow, elliptic to ovate; styles 3, connate proximally. Achenes included, dark brown to black, 3-gonous, 1.6-2.3 × 1.1-1.6 mm, shiny, smooth.

Ascending-erect, 15-60 cm high, glabrous, branched from base or above, annual herb. Stem brownish or reddish brown, glabrous, canaliculate. Leaves 2.5-12 x 0.75-3.5 cm, lanceolate-elliptic, acuminate, hairy, entire, with a rounded or cordate base, petiole 2-7 mm long. Ochrea 8-20 mm long, ovate, tubular, setose or ciliate, cilia almost equalling the ochreae or longer. Inflorescence very laxly flowered, interrupted 0.8-4.0 cm long, terminal-axillary raceme. Flowers up to 2.0 mm across, pedicel 1.0 mm long. Ochreolae 1.0-3.0 mm long, setose or ciliate, cilia 1.0-4.0 mm long. Tepals 5, biseriate, unequal, red, pink or whitish, ovate-obovate, obtuse. Stamens 5-8, filaments long. Ovary trigonous, rounded, with 3 styles, styles free above, fused below. Nuts trigonous, shining, black.

Himalaya (Kashmir to Nepal), N. Burma, China, Japan, Malaysia.

introduced; B.C., N.B., Ont.; Ala., Conn., Del., Fla., Ga., Ill., Ind., Iowa, Kans., Ky., La., Maine, Md., Mass., Mich., Minn., Miss., Mo., Nebr., N.J., N.Y., N.C., Ohio, Pa., S.C., Tenn., Tex., Vt., Va., W.Va., Wis.; e Asia; introduced also in Europe.

Distribution: Kashmir to Nepal, extending upto Japan through N. Myanmar and China.

2100-2400 m

Fl. Per.: May-August.

Flowering May-Oct.

Floodplain forests and woodlands, shorelines of ponds, moist roadsides, waste places; 0-300m.

A fairly common species from plains to 2500 m, grows in ditches, moist places. Often confused with Persicaria salicifolia (Brous. ex Willd.). See discussion under excluded species.

Polygonum longisetum Bruijn in F. A. W. Miquel, Pl. Jungh. 3: 307. 1854; Persicaria caespitosa (Blume) Nakai var. longiseta (Bruijn) C. F. Reed; Polygonum caespitosum Blume var. longisetum (Bruijn) Steward

Polygonum longisetum De Bruyn in Miq., Pl. Jungh. 307. 1854; Polygonum serrulatum auct. non Lag. 1817 sensu Hook.f., Fl. Brit. Ind. 1: 38. 1886; R. R. Stewart, Ann. Cat. Vasc. Pl. W. Pak. & Kashm. 212. 1972; Polygonum caespitosum Bl. var. longisetum (De Bruyn) Danser, Polyg. Nied. 170. 1927; Persicaria caespitosa var. longiseta (De Bruyn) C. F. Reed in Phytologia 63 (5): 410. 1987.

Persicaria longiseta is a species of flowering plant in the knotweed family known by the common names Oriental lady's thumb, bristly lady's thumb, Asiatic smartweed, long-bristled smartweed, low smartweed, Asiatic waterpepper, bristled knotweed, bunchy knotweed, and tufted knotweed. It is native to Asia (China, India, Russia, Japan, Malaysia, etc.), and it is present in North America and Europe as an introduced species and often a weed.

Persicaria longiseta is an annual herb with stems 30 to 80 centimeters (12–32 inches) long, sometimes reaching one meter (40 inches). The hairless, branching stems may root at lower nodes that come in contact with the substrate. The leaves are lance-shaped and up to 8 centimeters (3.2 inches) long by 3 cm (1.2 inches) wide. They have bristly ochrea. The inflorescence is an elongate cluster up to 8 centimeters (3.2 inches) long and contains many pink flowers. The fruit is a small, smooth achene.

In its native region this plant is a common weed of rice paddies. It was introduced to North America near Philadelphia around 1910 and probably spread via the railroads. It is present in much of the eastern United States and much of Canada. It grows in moist habitat types such as wetlands, as well as dry and upland habitat. It can be found in meadows, marshes, mudflats, riverbanks, floodplains, levees, and lowland and upland forests. It is invasive in some areas.

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