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Home/Species/ Mrs. Austin's Knotweed

Polygonum austiniae

Greene

Mrs. Austin's Knotweed

G4Apparently Secure Found in 1 roadless area NatureServe Explorer →
G4Apparently SecureGlobal Rank
UnknownThreat Impact
Identity
Unique IDELEMENT_GLOBAL.2.152977
Element CodePDPGN0L0X1
Record TypeSPECIES
ClassificationSpecies
Classification StatusStandard
Name CategoryVascular Plant
Endemicoccurs (regularly, as a native taxon) in multiple nations
KingdomPlantae
PhylumAnthophyta
ClassDicotyledoneae
OrderPolygonales
FamilyPolygonaceae
GenusPolygonum
Synonyms
Polygonum douglasii ssp. austinae(Greene) E. Murr.Polygonum douglasii ssp. austiniae(Greene) E. Murr.Polygonum douglasii var. austiniae(Greene) M.E. Jones
Other Common Names
Austin's Knotweed (EN) Renouée d'Austin (FR)
Concept Reference
Kartesz, J.T. 1994. A synonymized checklist of the vascular flora of the United States, Canada, and Greenland. 2nd edition. 2 vols. Timber Press, Portland, OR.
Taxonomic Comments
FNA (vol. 5, 2005) elevates Polygonum douglasii ssp. austiniae to full species as P. austiniae.
Conservation Status
Rank Method Rank calculation - Biotics v2
Review Date2025-12-19
Change Date1991-08-05
Edition Date2025-12-19
Edition AuthorsSoteropoulos (2025)
Threat ImpactUnknown
Range Extent200,000-2,500,000 square km (about 80,000-1,000,000 square miles)
Number of Occurrences21 - 300
Rank Reasons
Polygonum austiniae is a wide-ranging annual herb found in dry to moist flats on banks, sagebrush plains, and ponderosa pine forests. It occurs in western North America from Alberta and British Columbia, Canada south in the United States to Wyoming, Nevada, and California. There are at least 65, and likely over 81, occurrences rangewide, which face threats from grazing, rights-of-way maintenance, forestry management practices, recreational activities, invasive species, and other threats in some places. Monitoring of populations should be conducted to improve our understanding of reproduction, plant abundance, threats, and trends, as well as continuing conservation measures to protect the taxon.
Range Extent Comments
Polygonum austiniae occurs in western North America from Alberta and British Columbia, Canada south in the United States through western Montana to western Wyoming and east of the Cascades Mountains in eastern Washington and Oregon to northeastern California and northern Nevada (FNA 2005, Jepson Flora Project 2025, Weinmann et al. 2025). Range extent was estimated to be approximately 700,000 square kilometers using herbarium specimens, photo-based observations, and NatureServe Network occurrence data documented between 1994 and 2025 (GBIF 2025, iNaturalist 2025, NatureServe 2025, RARECAT 2025, SEINet 2025).
Occurrences Comments
By applying a 1 km separation distance to herbarium specimens, photo-based observations, and NatureServe Network occurrence data documented between 1994 and 2025, it is estimated that there are 65 occurrences rangewide (GBIF 2025, iNaturalist 2025, NatureServe 2025, RARECAT 2025, SEINet 2025). This diminutive annual is likely overlooked in photo-based observations, underrepresented in herbaria collections, not all collections are georeferenced, and anecdotal comments support the likelihood that there are over 81 occurrences rangewide. Also, the MNHP (2025) notes, "The probability of finding additional occurrences appears to be good since large areas of suitable habitat across western and central Montana remain unsurveyed for the species."
Threat Impact Comments
Although threats are not widely documented, this species is threatened by grazing, rights-of-way maintenance, forestry management practices, recreational activities (especially off-road vehicles), invasive species, and other threats in some places, though there is insufficient data, including anecdotal accounts, to understand scope and severity of threats for this species (MNHP 2025, NatureServe 2025).
Ecology & Habitat

Description

Austin's Knotweed is a sparsely hairy annual with erect stems that are 3-10 cm high and branched near their bases. The alternate, narrowly egg-shaped to elliptic leaves are 5-15 mm long and 1/2-1/3 as wide. The lower leaves have short petioles, while the upper leaves are sessile and smaller. There are small membranous sheaths, or stipules, surrounding the stem at the point of leaf attachment. Groups of 1-4 tiny, nodding flowers occur in the axils of all but the lowest leaves. Each flower has 5-8 stamens and 5 petal-like tepals that are 2-3 mm long and green with white or pink margins. The shiny black achenes are 3-sided and mostly 2-2.5 mm long.

Diagnostic Characteristics

There are many similar-appearing annual species of POLYGONUM. The typical P. DOUGLASII has leaves that are less than 1/3 as wide as they are long and achenes that are ca. 3 mm long. Many other species of POLYGONUM have erect flowers. A technical key and hand lens may be required for positive determination.

Habitat

Polygonum austiniae grows in "dry to moist flats on banks, sagebrush plains, and ponderosa pine forests" (FNA 2005).

Reproduction

This species flowers from June to September (FNA 2005).
Terrestrial Habitats
Forest - ConiferWoodland - ConiferShrubland/chaparral
Other Nations (2)
CanadaN2
ProvinceRankNative
AlbertaS1Yes
British ColumbiaS2Yes
United StatesN4
ProvinceRankNative
MontanaS3Yes
OregonSNRYes
NevadaS2Yes
WyomingS2Yes
CaliforniaSNRYes
IdahoSNRYes
WashingtonS1Yes
Threat Assessments
ThreatScopeSeverityTiming
2 - Agriculture & aquacultureUnknownUnknownUnknown
2.3 - Livestock farming & ranchingUnknownUnknownUnknown
4 - Transportation & service corridorsUnknownUnknownUnknown
5 - Biological resource useUnknownUnknownUnknown
5.3 - Logging & wood harvestingUnknownUnknownUnknown
6 - Human intrusions & disturbanceUnknownUnknownUnknown
6.1 - Recreational activitiesUnknownUnknownUnknown
8 - Invasive & other problematic species, genes & diseasesUnknownUnknownUnknown
8.1 - Invasive non-native/alien species/diseasesUnknownUnknownUnknown
8.1.1 - Unspecified speciesUnknownUnknownUnknown

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Plant Characteristics
DurationANNUAL
Economic Value (Genus)No
Roadless Areas (1)
Washington (1)
AreaForestAcres
Upper TucannonUmatilla National Forest12,485
References (14)
  1. Flora of North America Editorial Committee (FNA). 2002a. Flora of North America north of Mexico. Vol. 26. Magnoliophyta: Liliidae: Liliales and Orchidales. Oxford Univ. Press, New York. xxvi + 723 pp.
  2. Flora of North America Editorial Committee (FNA). 2005. Flora of North America north of Mexico. Vol. 5. Magnoliophyta: Caryophyllidae: Caryophyllales, Polygonales, and Plumbaginales. Oxford Univ. Press, New York. vii + 656 pp.
  3. Global Biodiversity Information Facility (GBIF). 2025. Global Biodiversity Information Facility (GBIF) data portal. Online. Available: https://www.gbif.org/ (accessed 2025).
  4. iNaturalist. 2025. Online. Available: https://www.inaturalist.org (accessed 2025).
  5. Jepson Flora Project (eds.) 2025. Jepson eFlora. Online. Available: https://ucjeps.berkeley.edu/eflora/ (accessed 2025).
  6. Kartesz, J.T. 1994. A synonymized checklist of the vascular flora of the United States, Canada, and Greenland. 2nd edition. 2 vols. Timber Press, Portland, OR.
  7. Kartesz, J.T. 1999. A synonymized checklist and atlas with biological attributes for the vascular flora of the United States, Canada, and Greenland. First edition. In: Kartesz, J.T., and C.A. Meacham. Synthesis of the North American Flora, Version 1.0. North Carolina Botanical Garden, Chapel Hill, N.C.
  8. Montana Natural Heritage Program (MNHP). 2025. Missoula Phlox — <i>Phlox missoulensis</i>. Montana Field Guide. Montana Natural Heritage Program. Available. Online: https://FieldGuide.mt.gov/speciesDetail.aspx?elcode=pdplm0d190 (accessed 31 January 2025).
  9. NatureServe. 2025. NatureServe Network Biodiversity Location Data. NatureServe, Arlington, Virginia.
  10. <p>NatureServe's Rapid Analysis of Rarity and Endangerment Conservation Assessment Tool (RARECAT). 2025. Version: 2.1.1 (released April 04, 2025).</p>
  11. Poole, J. M. and B. L. Heidel. 1993a. Sensitive plant surveys in the Big Belt and Elkhorn Mountains, Helena National Forest, Montana. Unpublished report to the Helena National Forest. Montana Natural Heritage Program. Helena, MT. 129 pp. plus printouts, maps.
  12. Southwest Environmental Information Network (SEINet). 2025. Collections Databases. Online. Available: https://swbiodiversity.org/seinet/collections/index.php (accessed 2025).
  13. Vanderhorst, J. and B. L. Heidel. 1995. Sensitive plant survey in the Tobacco Root Mountains, Madison County, Montana. Unpublished report to the Beaverhead and Deerlodge National Forests. Montana Natural Heritage Program. Helena, MT. 66 pp. plus appendices.
  14. Weinmann, F., P.F. Zika, D.E. Giblin, B. Legler. 2002+. Checklist of the Vascular Plants of Washington State. University of Washington Herbarium. Online. Available: http://biology.burke.washington.edu/herbarium/waflora/checklist.php (Accessed 2025).