Polygonum persicaria of Michigan Flora.

A widespread weed, naturalized from Europe, more common in disturbed habitats (gardens, roadsides, etc.) and in drier ground than customary for P. pensylvanica and P. lapathifolia, but in many places grows with them: moist or dry disturbed ground, shores, fields, ditches, borders of marshes. First collected as long ago as 1838 in Van Buren Co.

There is usually a dark blotch in the middle of the leaf, but such a mark is also found at times in other species, e.g., P. lapathifolia and P. hydropiperoides.