You may have been seeing these big white flowers along county highways for the past few weeks. They are native to much of the southeastern United States. They bloom from about mid-July into autumn.
This plant is a kind of hibiscus called rose mallow. It is sometimes called swamp rose mallow because it thrives close to water. It likes places of full sunshine along stream banks, ponds and wetland areas with few trees.
If planted at about a 2-feet spacing along a sunny pond bank, the rose mallow can make a pleasing if rather unkempt hedge. Butterflies, bees and other insect pollinators love the rose mallow. In Southeast Missouri, this wild hibiscus sometimes shows a plant with light pink flowers.