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Statewide IPM Program, University of California

Ladysthumb  (Polygonum persicaria)

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Life stages of Ladysthumb mature plants seedling flower purple-blotched leaves seeds

Ladysthumb is a summer annual broadleaf weed that grows in moist soil. It is found throughout California to an elevation of 5000 feet (1500 m) and often follows human disturbance and is weedy on agricultural land and in other disturbed, moist places. Ladysthumb seeds are an important source of food for many songbirds, waterfowl, and mammals and its leaves provide cover for wildlife.


Wet fields, areas subject to seasonal flooding, irrigation ditches, pastures, orchards, rice and grain fields, irrigated croplands, and around the edges of ponds, shallow lakes, marshes, and streams.


Cotyledons (seed leaves) are about 1/3 to 1/2 of an inch (8–12 mm) long and roughly 1/25 to 1/10 of an inch (1–3 mm) wide, dull green, narrowly football shaped to oblong, with short, glandular hairs on the edges near the base, and have short stalks that are fused at the base.

Mature plant

Mature plants often form large clumps. Leaves are lance to football shaped with a characteristic purplish blotch near the middle, and about 1 to 8 inches (2.5–20 cm) long. Leaves are hairless to sparsely covered with minute, stiff hairs, and are alternate to one another along the stem. Stems are erect or spreading and range from 1 to 3 feet (30–100 cm) long. Stems can initiate roots at lower stem joints (nodes). Sheaths are tipped with short stiff hairs and leaves are either hairless or covered with short stiff hairs. Pale smartweed, P. lapathifolium, and ladysthumb look similar, but pale smartweed lacks the purple leaf blotch and short hairs on leaf sheaths that are characteristic in ladysthumb.


Small, pink, flowers densely cluster along erect terminal spikes that are about 1 inch (2.5 cm) long. Although similar in appearance, ladysthumb flowers are darker in color and do not droop as much as pale smartweed flowers. Flowers of the ladysthumb spike open; those of pale smartweed remain closed.


Fruits are brown to black, glossy, one seeded, broadly egg shaped, more-or-less three sided, and less than 1/12 of an inch (2 mm) long.


Reproduces by seed.

Related or similar plants

  • Pale smartweed, Polygonum lapathifolium

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