Possibly identified as
Motherwort

Tiny white blooms grow in rings around stem just above leaves.

Leaf edges are jagged and grow in sets of opposing pairs.

The plants grow 12" to 18" tall here and bloomed in early August.

 
     
         
Photos by Lauren Hawkins, 8/03
 
Various stages of growth are visible in these summer views of flora on wetland prairie near the Town Branch of the West Fork of the White River in Fayetteville, Arkansas
         
Many thanks to Carl Hunter
and his widely known, authoritative books "Trees of Arkansas" and "Wildflowers of Arkansas" and their invaluable help identifying these plants.
Hunter's best guess by judging by these photos is found on page 188 in "Wildflowers of Arkansas".