Scientific Name: Polygonum persicaria
Family Name: Polygonaceae
Leaf: 2 6 in. (5 15 cm.) long, green, lanceolate leaves with a dark green oval in the center of each leaf.
Plant: 8 31 in. (20 80 cm.) tall with pink stems. Most of the height comes from the cylindrical spike of flowers.
Identifying Characteristics: Lady's Thumb is very similar to Pink Knotweed, Polygonum pensylvanicum. The only feature that differentiates them is the dark green oval on the center of each Lady's Thumb leaf.
Location: We found Lady's Thumb growing on the edge of the path through Cold Spring Park in Newton, Massachusetts.
History and Comments: Lady's Thumb is native to Europe. It is unclear how it reached the United States, but it probably invaded before 1850. Lady's Thumb is so called, because of the dark green splotch on the leaf, which supposedly resembles a lady's thumb.