Scientific NamePolygonum persicaria
Other Common Names:
lady's thumb smartweed
Synonyms (former Scientific Names):
Polygonum persicaria var. ruderale
Polygonum persicaria var. angustifolium
This erect summer annual flowers from July to October. It can grow up to 3 1/2 feet in height with numerous branches.
The alternately arranged leaves are lance to egg shaped, and grow from 2 to 6 inches long and can be up to 2 inches wide. The leaves have a hairy upper surface, and margins, while the lower surface remains smooth. The leaves often have a purple mark in the center, resembling a lady's thumb.
A membranous sheath or ocrea surrounds the base of each petiole. This species has stiff hairs arising from the top of each ocrea.
Flower Seed Head
The pink or white flowers are usually grouped in terminal spikes on the ends of long, hairy stems.
Each seed is enclosed in an achene. The achenes are a glossy black, and are circular to oval, 2.5 to 3.5 mm wide.
This plant prefers moist soil.
upright and nonwoody
Thorns or Spines
Approximate Flower Diameter
Dominant Flower Color
shorter than leaf
Stem Cross Section
round or oval