Prunus is the genus that includes stone fruit species like peaches, nectarines, plums, and cherries. Even though these common species are grown widely in North America, they are not native here. However, there are several native Prunus that can be found in the wild.
This link http://plants.usda.gov/java/stateSearch?searchTxt=prunus&searchType=Sciname&stateSelect=US28&searchOrder=1&imageField.x=0&imageField.y=0 shows all the Prunus species in Mississippi.
A common species in Mississippi is the American plum (Prunus americana) http://www.duke.edu/~cwcook/trees/pram.html. Other species exist such as hog plum (Prunus umbellata) http://www.duke.edu/~cwcook/trees/prum.html and can be found with some looking.
Virginia Cooperative Extension just published a nice fact sheet on native fruit and nut trees (http://pubs.ext.vt.edu/ANR/ANR-23/ANR-23NP_pdf.pdf). If you have never seen a native plum tree, I just happen to have some photos (see below). These were provided by Jim Giles of Rankin Co., MS.
The question often asked, “Is it edible?” The answer is yes. These types of plums are often used for processing into jams and jellies or even wine. Of course, as with any wild plant, some individuals will produce better flavored fruit than others. Native plums can vary in tree size and shape. Some are trees, but many develop into thickets and may have “thorns”. Usually the trees will get to 15 or 20 ft tall at most. Fruit color can also vary from purple to peach-like. Often there is a strong “bloom” or wax on the skin.
Overall, native Prunus can be found in many states. They provide excellent forage for animals, but with a little management, can be good sources of fruit for humans as well.