Whether for a water feature, landscape plan, rain garden or watershed planting plan, wetland plants provide practical beauty. Identification of suitable wetland plants for these areas provides lessons in the diversity of plant life on Earth that dwarfs the choices faced for a perennial border. Intriguing ancient plants, delicate wildflowers and graceful grasses all inhabit the wetlands. Rather than fill in that low area along the back of your property, consider preserving existing wetlands and their flora.
We live on a planet where life is dependent upon water and oxygen. The areas where rain falls on its surface are either aquifers---the land that filters water downward to storage in water tables---or watersheds---the areas that drain floods and excess water back to the seas. Located throughout these areas and at their intersections are wetlands---areas that stay wet for most of the year. They provide homes for a vast variety of plant life that produces oxygen and helps manage the movement of water across the face of the planet. The U.S. Environmental Protection Agency estimates that the United States loses about 60,000 acres of wetlands annually---a critical reduction of a vital resource.
Wetland plants grow in specialized environments that give hints for their identification. Saw grass grows in coastal salt marshes while cattails grow inland in freshwater marshes. Although all wetlands have soil that lacks oxygen, plants that grow in wetlands have preferences for the variety of wetland they inhabit. Note whether plants prefer bogs, where little open water appears, marshes with areas of open water, swamps with wide areas of open water, or river or stream floodplains that flood periodically but are dry at times.
Like other plants, wetland plants have varying degrees of hardiness---the range of temperatures they can endure. The hardiest grasses grow where winter temperatures dip below zero degrees F. Cardinal flowers and lotuses are less hardy and can be found where winters are mild or the climate is tropical. Varieties of water lily thrive over a wide area, from the warm Southeast to the cold Upper Midwest of the United States. A growing zone map from the U.S. National Arboretum or U.S. Department of Agriculture documents areas with similar climates.
Both vascular and non-vascular plants grow in wetlands. Non-vascular plants such as mosses and algae have no biological system to carry water throughout the plant; they are are well-suited to wet areas. The majority of wetland plants are vascular angiosperms, though. Submergent plants, such as water milfoil, coattail and eel grass, grow entirely under the surface of the water. Floating plants, including lotus, water lilies, duckweed and spatterdock, prefer calm waters. Emergent plants---cattails, arrowhead, willows, marsh marigolds and pickerelweed---bloom along banks or grow in shallow water.
All wetland plants have adapted to growth in low-oxygen, high-moisture laden soil. Some have adapted too well. Some plants have spread beyond areas where they are native to invade wetlands and crowd out indigenous plants, upsetting the balance of water retention as well as oxygen and food production in the environment. Avoid plants such as purple loosestrife, leafy spurge and wild parsnip, which, although hardy and attractive, may endanger native plants and the living things that depend on them.