Marsh Elder, iva frutescens, is a very common species on Dewees Island.  Also known as the high tide bush, it grows on the outer coastal plain, and is a fleshy perennial that grows 3-6 feet tall.  It can tolerate some salinity and the occasional wash-over of brackish water.  It is commonly found with sea oxeye daisy and salt myrtle or groundsel, and together they form what Porcher calls the “salt marsh thicket.”

http://www.nativeplantcenter.net/?q=plants/387