Scientific Name: Polygonum lapathifolium

Common Name: curlytop knotweed

Other Common Names: curltop ladysthumb, pale smartweed

Synonyms: Persicaria incarnata, Persicaria lapathifolia , Persicaria tomentosa, Polygonum incarnatum, Polygonum incanum, Polygonum nodosum, Polygonum oneilli, Polygonum pensylvanicum, Polygonum scabrum, Polygonum tomentosum

Habit: This erect summer annual can grow from 3 to 5 feet tall, and can be found flowering from June through October.

Leaves: The leaves are generally lance shaped with smooth margins. The whitish undersides have minute sunken glands, while the upper surface remains smooth. Stems are connected to the stalk by thick sheaths.

Identifying Characteristics: Pale smartweed is very similar to Lady's Thumb, but can be distinguished by the hair on the lower surfaces of its leaves, and by the lack of hairs on the upper edge of the leaf sheaths.

Flower Seed Head: The white to pale pink flowers can be found on 1 to 3 inch long stalks in dense, hanging spikes. Each 5-petaled flower never opens, and is insect or self pollinated.

Seed Fruit: The seeds develop in an ovate, flattened achene that is slightly concave on either side. Each achene can grow up to 2 mm in length. The individual seeds are shiny, lens shaped, and black.

Where Found: Pale smartweed prefers loose, rich, acidic soils high in organic matter. It can be found in wet environments such as areas near ponds, streams, wet fields, and waste places.

  • Life cycle: summer annual

  • Plant type: Herb

  • Thorns: Not Present

  • Plant family: Polygonaceae

  • Leaf arrangement: alternate

  • Leaf shape: lance

  • Ochrea: Present

  • Leaf margin: entire

  • Stem hairs: has hairs; no hairs

  • Flower color: purple; pink; white

  • Growth habit: upright and nonwoody

  • Stem: round or oval

  • Leaf structure: simple

  • Leaf hairs: has hairs

  • Flower diameter: pencil

  • Root structure: fibrous

  • Leaf stalk: shorter than leaf