Bristly Smartweed

Persicaria setacea (Baldw.) Small

Persicaria setacea plants
Robert Mohlenbrock, USDA-NRCS PLANTS database

Dicotyledoneae (Dicots)
Polygonaceae (Buckwheat Family)
State Protection
Listed as Endangered by New York State: in imminent danger of extirpation in New York. For animals, taking, importation, transportation, or possession is prohibited, except under license or permit. For plants, removal or damage without the consent of the landowner is prohibited.
Federal Protection
Not Listed
State Conservation Status Rank
Critically Imperiled or Imperiled in New York - Especially or very vulnerable to disappearing from New York due to rarity or other factors; typically 20 or fewer populations or locations in New York, very few individuals, very restricted range, few remaining acres (or miles of stream), and/or steep declines. More information is needed to assign either S1 or S2.
Global Conservation Status Rank
Secure globally - Common in the world; widespread and abundant (but may be rare in some parts of its range).


Did you know?

The bristly hairs on the margin of the membrane surrounding the stem at the base of the leaf (ochrea) give this plant its species name (Fernald 1950).

State Ranking Justification

There are four existing populations but all of them have 100 plants or fewer. There are 22 additional historical records from the late 1800s through the 1950s which need to be resurveyed. One population no longer exists because its habitat has been destroyed.

Short-term Trends

The short-term trend is unknown due to an insufficient number of recent surveys.

Long-term Trends

The long-term trend of this species is apparently strongly negative. It seems to have severely declined over the last 100 years although more surveys are needed to confirm this.

Conservation and Management


There are currently no known threats.

Conservation Strategies and Management Practices

Establish and maintain natural buffers around the wetlands where this species occurs to preserve the natural hydrology and to keep out wetland invasive species.

Research Needs

More research is needed into the habitat preference of this species since it occurs in small numbers in large wetland complexes.



In New York this species occurs in a variety of wetlands from pond shores to open marshes, ditches, and stream corridors within red maple swamps. It has not been found in coniferous wetlands (New York Natural Heritage Program 2012). Marshes and shallow water (Gleason and Cronquist 1991). Alluvial woods and swamp forests (FNA 2005).

Associated Ecological Communities

  • Coastal plain pond shore (guide)
    The gently sloping shore of a coastal plain pond with seasonally and annually fluctuating water levels. Plants growing on the pond shore vary with water levels. In dry years when water levels are low there is often a dense growth of annual sedges, grasses, and herbs. Submerged and floating-leaved aquatic plants, such as fragrant waterlily and pondweeds, may become "stranded" on the exposed shore. In wet years when the water level is high only a few emergents and floating-leaved aquatics may be noticeable. T
  • Ditch/artificial intermittent stream
    The aquatic community of an artificial waterway constructed for drainage or irrigation of adjacent lands. Water levels either fluctuate in response to variations in precipitation and groundwater levels, or water levels are artificially controlled.
  • Red maple-hardwood swamp (guide)
    A hardwood swamp that occurs in poorly drained depressions, usually on inorganic soils. Red maple is usually the most abundant canopy tree, but it can also be codominant with white, green, or black ash; white or slippery elm; yellow birch; and swamp white oak.
  • Shallow emergent marsh (guide)
    A marsh meadow community that occurs on soils that are permanently saturated and seasonally flooded. This marsh is better drained than a deep emergent marsh; water depths may range from 6 in to 3.3 ft (15 cm to 1 m) during flood stages, but the water level usually drops by mid to late summer and the soil is exposed during an average year.

Associated Species

  • Acer rubrum
  • Chamaedaphne calyculata (leatherleaf)


New York State Distribution

This wetland herb ranges from Long Island across New York south of the Adirondacks. It is absent from the Southern Tier and many counties in eastern New York.

Global Distribution

It is most common in the south central and southeastern US with scattered populations north to the Midwest, New York and Massachusetts where is considered rare. It also extends south from Texas into Latin America.

Identification Comments

General Description

Swamp smartweed is a robust perennial wetland wildflower that grows up to 1.5 meters tall from a tough, woody rhizome. Lanceolate leaves, 7-20 cm long and somewhat hairy, grow from strongly swollen nodes. The ochrea (stem sheath above the base of the leaf) is brown and papery in texture, with flat margins topped by bristles 6-12 mm long. The surface of the ochrea has long, ascending to spreading hairs, at least at the top. The hairs are attached to the ochrea only one third of their length and spread out along the remainder. The inflorescence is more or less erect and not drooping. The small greenish-white to creamy tan flowers are smooth and not glandular-punctate. The peduncles are without stalked glands. The achene is 2-3 mm long, brown to black and lustrous (FNA 2005).

Identifying Characteristics

Distinguishing characteristics: robust perennial with elongate horizontal rhizomes, occasionally stoloniferous in water; the erect stem 2.5-6 mm thick at base, simple or more commonly branching from the middle and upper nodes, 40-150 cm tall; ocreae remotely strigose, bearing marginal closely ascending bristles 5-15 mm long; upper leaf surface with short stiff hairs 0.2-0.5 (0.8) mm long, strigose; lower leaf surface similarly strigose to glabrous; primary leaves 7-18 cm long and 1.2-3.5 cm broad; calyx at maturity 3-3.5 mm long, the sepals white; flowers greenish-white to creamy-tan; achene 2-3 mm long, trigonous, lustrous. Best life stage for ID: in flower. Characteristics needed to ID: entire plant with stem, leaves and flowers.

Best Life Stage for Proper Identification

The best time to identify this species is when it is in flower or fruit.

Similar Species

The very similar and common species Persicaria hydropiperoides, mild water pepper, has more slender stems, flowers that are usually pink to rose colored (sometimes they can be whitish) and ochrea with hairs that are pressed to the stem for usually half to two thirds their length. Persicaria amphibia, water smartweed, has dense spikes of deep rose colored flowers and usually occurs in deeper water (FNA 2005).

Best Time to See

Flowers and fruits present from August until early fall.

  • Flowering
  • Fruiting

The time of year you would expect to find Bristly Smartweed flowering and fruiting in New York.

Bristly Smartweed Images


Bristly Smartweed
Persicaria setacea (Baldw.) Small

  • Kingdom Plantae
    • Phylum Anthophyta
      • Class Dicotyledoneae (Dicots)
        • Order Polygonales
          • Family Polygonaceae (Buckwheat Family)

Additional Common Names

  • Swamp Smartweed


  • Polygonum hydropiperoides var. setaceum (Baldw.) Gleason [in part.]
  • Polygonum setaceum Baldw.
  • Polygonum setaceum var. setaceum
  • Polygonum setaceum var. tonsum Fernald

Additional Resources

Best Identification Reference

Flora of North America Editorial Committee. 2005. Flora of North America North of Mexico, Volume 5, Magnoliophyta: Caryophyllidae, Part 2. Oxford University Press, New York.

Other References

Crow, Garrett E. and C. Barre Hellquist. 2000. Aquatic and Wetland Plants of Northeastern North America: A revised and enlarged edition of Norman C. Fassett's a Manual of Aquatic Plants. Volume One: Pteridophytes, Gymnosperms, and Angiosperms: Dicotyledons. The University of Wisconsin Press. Madison, Wisconsin. 536 Pages.

Fernald, M.L. 1950. Gray's manual of botany. 8th edition. D. Van Nostrand, New York. 1632 pp.

Gleason, Henry A. and A. Cronquist. 1991. Manual of Vascular Plants of Northeastern United States and Adjacent Canada. The New York Botanical Garden, Bronx, New York. 910 pp.

Holmgren, Noel. 1998. The Illustrated Companion to Gleason and Cronquist's Manual. Illustrations of the Vascular Plants of Northeastern United States and Adjacent Canada. The New York Botanical Garden, Bronx, New York.

House, Homer D. 1924. Annotated list of the ferns and flowering plants of New York State. New York State Museum Bulletin 254:1-758.

Mitchell, Richard S. and Gordon C. Tucker. 1997. Revised Checklist of New York State Plants. Contributions to a Flora of New York State. Checklist IV. Bulletin No. 490. New York State Museum. Albany, NY. 400 pp.

Mitchell, Richard S. and J. Kenneth Dean. 1978. Polygonaceae (buckwheat family) of New York State. Contributions to a flora of New York State. Richard S. Mitchell, ed. New York State Museum Bulletin No. 431. 79 pp.

New York Natural Heritage Program. 2010. Biotics database. New York Natural Heritage Program. New York State Department of Environmental Conservation. Albany, NY.

New York Natural Heritage Program. 2024. New York Natural Heritage Program Databases. Albany, NY.

Smith, Gerald A. No date. Bird breeding season survey at El Dorado Beach Preserve 1981-.

Weldy, T. and D. Werier. 2010. New York flora atlas. [S.M. Landry, K.N. Campbell, and L.D. Mabe (original application development), Florida Center for Community Design and Research University of South Florida]. New York Flora Association, Albany, New York


About This Guide

This guide was authored by: Stephen M. Young

Information for this guide was last updated on: September 20, 2012

Please cite this page as:
New York Natural Heritage Program. 2024. Online Conservation Guide for Persicaria setacea. Available from: Accessed July 19, 2024.