This naturalized annual was introduced from Europe. The erect stems, up to 3 feet tall, bear lance-shaped leaves up to 6 inches long, usually with a dark purplish spot or crescent near the middle of each leaf (A,B,C). The small pink flowers on cylindrical spikes are on erect stems above the leaves (A). Differentiated from similar species by the purple spot or crescent on the leaves. Pennsylvania Smartweed (Polygonum pensylvanicum) – not shown here – looks very similar, but it never has those purple spots on the leaves.
Grows in dense colonies on floodplains, flowering from June through September. In Fontenelle Forest, common below the blind at the end of the Gifford Memorial Boardwalk. At Neale Woods, uncommon near Pond Trail on the south side of pond.
Apparently whoever named this plant thought the spot near the middle of the leaves resembled a lady’s thumbprint.
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