John, the most appropriate wetland species to plant in your constructed wetland are those that are indigenous to your geographic area. I recommend that you visit some natural wetlands in your area and prepare a list of the wetland species that are most appealing to your individual taste. Select a diversity of species with varying colors, textures, sizes, and growth habits.
After you have selected the species you wish to plant, design a planting scheme that mimics the natural wetlands in your area. You may be able to obtain a permit to collect the clumps of wetland plants from State, or US Forest Service lands. If that is not an option, seek permission from a rural landowner to dig the required planting material from natural wetlands on private land.
This is the method that I use. I inform the landowner about the intended use of these plants, and have found that they are very interested in the technology, and are enthusiastic to participate in the project by contributing the plants. You may wish to include some flowering species that may not be native to your area.
Several different species adds to the aesthetic beauty of the final product. Good luck in your quest to vegetate your constructed wetland, and keep in mind that the most important role of the vegetation is that they provide for a pleasing landscaping amenity. JWA