This section is from the book "Who's Who Among The Wild Flowers", by W. I. Beecroft. Also available from Amazon: A Field Guide to Edible Wild Plants.
Common Persicaria: Jointweed.
Polygonum pennsylvanicum.
Buckwheat Family. July - Sept.
A plant of sprawling, branching habit, 1 - 3 feet high, common in waste places, moist soil.
Pink or greenish, small, crowded on short, narrow, terminal spikes.
Long, narrow, toothless, tapering toward the tip. Plant stems enlarged at the joints.

Pink Knotweed.
Polygonum Persicaria.
Is a similar species, leaves usually marked with a dark triangle. Found throughout North America. Naturalized from Europe.
 
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