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.
Yellow Wood-sorrel.
Oxalis corniculata.
Wood Sorrel Family. May - Sept.
Common weed in all situations. Nova Scotia to Gulf, west to Dakota.
Yellow, small, 5 divisions.
Composed of 3 heart-shaped leaflets.

Lady's Sorrel.
 
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