The Illinois Wildflowers site notes that seedbox or rattlebox has the showiest flowers among Ludwigias. True in Illinois or Michigan, but a little farther south there are a lot of species that look a lot like this. They mostly grow in damp areas or even in water, and many are called water-willows. The pods, when mature and dry, do rattle. This one gets aaround two feet tall, and has lance-shaped leaves. It's just very prettily average. Seedbox was once listed as a threatened species in Michigan, where it is at the northern limit of its range. Enough has now been found that it is off the list. Seedbox grows in AL, AR, CT, DE, FL, GA, IA, IL, IN, KS, KY, LA, MA, MD, MI, MO, MS, NC, NE, NJ, NY, OH, OK, PA, RI, SC, TN, TX, VA, VT, WI, WV, ON, and QC. Lucas Co OH, 7/14/13. Willowherb family, Onagraceae.