Lady's Thumb

Smartweed (Polygonaceae family):

Persicaria maculosa Gray

EPPO code:

POLPE

Other names:

Red shank, smartweed

Species information

Lifecycle:

Annual.

Propagation:

Reproduces by seed.

Emergence:

Germinates and emerges early in the spring.

Habitat:

Lady’s thumb can be found throughout Ontario, although it is most often found in cultivated crops, waste places and open fields. The plant establishes in all types of soil.

Competitiveness:

Agriculture and Agri-Food Canada research has shown that lady’s thumb densities of 20,000 plants/ac can result in 13–15 percent yield loss in corn and soybeans.

Identification clues

Seedling

Cotyledons:

Oblong tapering into a short stalk, sometimes reddish purple underneath.

First leaves:

Lady’s thumb has elongated, alternate first leaves, often with black dots on the upper surface. Sometimes it has a black, triangular imprint, referred to as the “thumb mark,” which gives the plant its common name.

Mature leaves:

Appear similar to younger leaves with alternate leaf orientation. Leaves are elongated and have wavy margins, as well as the black “thumb mark.”

Mature plant

Stems:

The stems of lady’s thumb are erect and smooth, and range in colour from red to reddish-green to green. The membranous sheath surrounding the stem at each node, called the ocrea, is hairy.

Flowers:

Lady’s thumb flowers are small, each with five pinkish-white to pink sepals. The flowers are dense and crowded into narrow, cylindrical spikes.

Seeds:

The plant’s seeds are smooth, shiny black, typically flat, and oval with a pointed tip. Individual seeds are about 2 mm in diameter.

Roots:

Taproot.

Often mistaken for

I know it's not Pale/green smartweed because the ocrea of lady’s thumb is covered in short hairs and has a fringe of hairs on the top margin whereas the ocrea of pale/green smartweed is hairless.