Right Answer:
You can tell this is Common Smartweed because of the small pinkish flowers that are located at the end of the stems of the plant.  Common Smartweed generally has a slightly reddish stem.  The stems of this plant sometimes reach a length of 5 feet but are very weak and trail along the ground.  The nodes of the plant are generally swollen and the leaves are shaped like a peach trees leaves. The seeds of the plant are purplish-black to black in color and flattened.  One side of the seed there is a projection.    
 
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