Minnesota Seasons - Curlytop Knotweed

Conservation • Wetland • Description • Habitat • Ecology • Use • Distribution • Taxonomy

Conservation Status

IUCN Red List

LC - Least Concern

NatureServe

N5 - Secure

SNR - Unranked

Minnesota

not listed

Wetland Indicator Status
Great Plains	OBL - Obligate wetland
Midwest	FACW - Facultative wetland
Northcentral & Northeast	FACW - Facultative wetland

Description

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 ⅝″ 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 3⅛″ 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 ⅛″ 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 ⅛″ wide achene. The achene is flattened or concave on both sides.

Height

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.

Habitat

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

Ecology

Flowering

July to September

Pests and Diseases

Use

Distribution
		Sources 2, 3, 5, 7, 24, 28, 29, 30. Biodiversity occurrence data published by: Minnesota Biodiversity Atlas (accessed through the Minnesota Biodiversity Atlas Portal, bellatlas.umn.edu,9/6/2025).
9/6/2025

Nativity
Native

Occurrence
Common

Taxonomy
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) / Angiospermae (flowering plants)
Class	Magnoliopsida (flowering plants)
Superorder	Caryophyllanae
Order	Caryophyllales (pinks, cactuses, and allies)
Family	Polygonaceae (knotweed)
Subfamily	Polygonoideae
Tribe	Persicarieae
Subtribe	Persicariinae
Genus	Persicaria (knotweeds, smartweeds, and waterpeppers)

Subordinate Taxa
More than 24 subspecies, varieties, or forms (infraspecific taxa) of Persicaria lapathifolia have been described. However, most do not recognize any infraspecific taxa.

Synonyms
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 heart’s-ease nodding smartweed pale persicaria pale smartweed smartweed willow weed

Glossary

Achene

A dry, one-chambered, single-seeded seed capsule, 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.

Axil

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

Fascicle

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

Node

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

Ocrea

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

Petiole

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.

Raceme

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

Sepal

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

Sheath

The lower part of the leaf that surrounds the stem.

Stipule

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.

Tepal

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.