Water primrose has waxy, oblong leaves with pronounced veins and smooth edges. Its stems have a reddish tinge, especially in later summer, and often stand up off the water’s surface. Between late July and early September, water primrose produces yellow flowers about one inch across.
notice how Ludwigia has both round AND pointed leaves, as well as the 5-petaled flower
note the red stems common to both native and non-native Ludwigia species