curlytop knotweed

(Persicaria lapathifolia)

Conservation Status
curlytop knotweed
  IUCN Red List

LC - Least Concern


N5 - Secure

SNR - Unranked


not listed

Wetland Indicator Status
  Great Plains

OBL - Obligate wetland


FACW - Facultative wetland

  Northcentral & Northeast

FACW - Facultative wetland


Curlytop knotweed, also called pale smartweed, is a 24 to 60 tall, erect, annual forb that rises from a taproot and shallow, fibrous roots.

The stems are ascending to erect, occasionally branched, round, and hairless. They are conspicuously swollen at the leaf nodes.The Latin word polygonum is derived from Greek and means "many knees or joints", referring to the swollen nodes.

The leaves are alternate, variable in shape but usually lance-shaped, 1½ to 4¾ long, and 3 16 to 1½ wide. They are on leaf stalks up to long. The leaf stalks wrap around the stem with a membranous sheath (ocrea) at the base. The ocrea is hairless and does not have a fringe of hairs or bristles on the margin. It turns brown as the leaf matures and eventually peels away. The leaf blades are tapered or wedge-shaped at the base and taper to a point at the tip with concave sides along the tip. The upper surface is hairless. The lower surface is usually hairless, sometimes covered with short, soft, woolly hairs, especially when young. The margins are untoothed. There is sometimes a dark blotch in the middle of the leaf blade, but it is neither as common nor as prominent as with spotted lady’s thumb.

The inflorescence is an unbranched, spike-like cluster (raceme) at the end of the stem and branches and sometimes also rising from the upper leaf axils. The racemes are arching or nodding, robust, dense, 1¼ to 3 long, and 3 16 to ½ wide. They are usually not interrupted. The flowers are arranged in several bundles (fascicles) with 4 to 14 flowers each. The fascicles are sheathed at the base and the sheaths overlap.

Individual flowers are 1 16 to long. There are 5 sepals and no petals (5 tepals). The tepals are fused at the base. The outer 2 or 3 tepals are egg-shaped to elliptic, usually greenish-white, sometimes pink, with prominent, anchor-shaped veins. There are 5 or 6 stamens and 2 or 3 styles. The stamens have pink or red anthers. The styles are fused at the base. The flowers rarely open, so the stamens, styles, and inner tepals are difficult to see. There is no fragrance.

The fruit is dark brown to black, oval, 1 16 to wide achene. The achene is flattened or concave on both sides.




24 to 60


Flower Color


Greenish-white to pink


Similar Species


Pennsylvania smartweed (Persicaria pensylvanica) racemes are mostly held erect, rarely nodding. The flowers are often pink.

Spotted lady’s thumb (Persicaria maculosa) is a smaller plant, no more than 32 in height. The ocrea has a few short hairs on the margin. There is usually a prominent, dark blotch in the middle of the leaf blade. The flowers are pink to rose.


Wet to moist. Lake shores, pond edges, marshes, wet prairies, ditches, railroads, roadsides, gravel bars, disturbed sites. Full to partial sun.




July to September


Pests and Diseases






Distribution Map



2, 3, 4, 5, 7, 24, 28, 29, 30.









  Kingdom Plantae (green algae and land plants)  
  Subkingdom Viridiplantae (green plants)  
  Infrakingdom Streptophyta (land plants and green algae)  
  Superdivision Embryophyta (land plants)  
  Division Tracheophyta (vascular plants)  
  Subdivision Spermatophytina (seed plants)  
  Class Magnoliopsida (flowering plants)  
  Superorder Caryophyllanae  


Caryophyllales (pinks, cactuses, and allies)  


Polygonaceae (knotweed)  
  Subfamily Polygonoideae  
  Tribe Persicarieae  
  Subtribe Persicariinae  


Persicaria (knotweeds, smartweeds, and waterpeppers)  

Subordinate Taxa






Persicaria incarnata

Persicaria tomentosa

Polygonum incanum

Polygonum incarnatum

Polygonum lapathifolium

Polygonum lapathifolium var. incanum

Polygonum lapathifolium var. nodosum

Polygonum lapathifolium var. ovatum

Polygonum lapathifolium ssp. pallidum

Polygonum lapathifolium var. prostratum

Polygonum lapathifolium var. salicifolium

Polygonum nodosum

Polygonum oneillii

Polygonum pensylvanicum ssp. oneillii

Polygonum scabrum

Polygonum tomentosum


Common Names


curltop ladysthumb

curlytop knotweed

curlytop smartweed

dock-leaf smartweed

dock-leaved smartweed


nodding smartweed

pale persicaria

pale smartweed


willow weed













A dry, one-chambered, single-seeded fruit, formed from a single carpel, with the seed attached to the membranous outer layer (wall) only by the seed stalk; the wall, formed entirely from the wall of the superior ovary, does not split open at maturity, but relies on decay or predation to release the contents.



The upper angle where a branch, stem, leaf stalk, or vein diverges.



A small bundle or cluster, often sheathed at the base, as with pine needles.



The small swelling of the stem from which one or more leaves, branches, or buds originate.



A sheath around the stem at the base of a petiole formed from the stipules; a feature of many members of the Polygonaceae.



On plants: The stalk of a leaf blade or a compound leaf that attaches it to the stem. On ants and wasps: The constricted first one or two segments of the rear part of the body.



An unbranched, elongated inflorescence with stalked flowers. The flowers mature from the bottom up.



An outer floral leaf, usually green but sometimes colored, at the base of a flower.



The lower part of the leaf that surrounds the stem.



A small, leaf-like, scale-like, glandular, or rarely spiny appendage found at the base of a leaf stalk, usually occurring in pairs and usually dropping soon.



Refers to both the petals and the sepals of a flower when they are similar in appearance and difficult to tell apart. Tepals are common in lilies and tulips.

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Bill Reynolds

    curlytop knotweed      


    curlytop knotweed   curlytop knotweed  
    curlytop knotweed      


    curlytop knotweed   curlytop knotweed  


    curlytop knotweed   curlytop knotweed  

Compare Pennsylvania smartweed on the left with curlytop knotweed on the right

    Pennsylvania smartweed      



  Persicaria lapathifolia (Nodding Smartweed)
Allen Chartier
  Persicaria lapathifolia (Nodding Smartweed) (  



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Other Videos
  Pale Persicaria (Persicaria Lapathifolia L.) - 2012-09-02

Published on Sep 5, 2012

Pale Persicaria (Persicaria lapathifolia (L.) Delarbre, syn. Polygonum lapathifolium L.) is a plant of the family Polygonaceae. It is closely related to Redshank and as such is considered a weed in Britain and Europe.

Other common names for the plant include pale smartweed, curlytop knotweed, and willow weed.

De beklierde duizendknoop (Persicaria lapathifolia, basioniem: Polygonum lapathifolium), knopige duizendknoop of Bleek knoopkruid is een algemeen voorkomende, eenjarige plant uit de duizendknoopfamilie (Polygonaceae).

  European Honeybee on Persicaria セイヨウミツバチ♀がオオイヌタデを訪花採餌

Published on Dec 26, 2014

Foraging workers of European honey bee (Apis mellifera, family Apidae) visiting pink flowers of (Persicaria lapathifolia, family Polygonaceae) for nectar and pollen. Mid-September 2014 in Japan.


  Curlytop Knotweed, オオイヌタデ
Koji Kimura

Published on Sep 7, 2013

Curlytop Knotweed, オオイヌタデ




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Location: Pennington County

curlytop knotweed  




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