Over 1,400 species of wetland plants grow in the United States. The vast majority of these plants are native, though a growing number are introductions from Europe and Asia; several heavy-hitters have established themselves as dangerous invasives. Because of the huge variety of native species, a well-illustrated native plant guide is the best tool for identifying native aquatic plants. Several natives and non-natives stand out, however, and can be easily picked out of wetland scenes in most parts of the country.
Types of Aquatic Plants
All aquatic plants, whether native or non-native, have only three types of leaves. Submersed plants grow with their leaves completely beneath the surface of the water, emersed plants have leaves and stems that grow above the surface of the water and floating leaf plants' foliage rests directly on the surface of the water. Aquatic plants also grow with their roots in a variety of locations---anchored in mud beneath the water, free floating or in waterlogged soils.
Native Submersed Plants
One common characteristic of submersed plants are their flaccid stems. One of two commonly submersed plant species is sago pondweed (Potamogeton pectinatus), which grows in both still and flowing waters and is readily identifiable by its multi-stemmed branches and long, needle-like leaves.
Bladderworts (Utricularia species) grow across the entire North American continent and are named for the tiny air pouches that keep them afloat. Bladderworts send a flower stalk with one irregularly shaped yellow flower above the water line to reproduce. Branches are multi-stemmed, radiating in a circle from the main stem.
Native Emersed Plants
Most people are familiar with the ubiquitous cattail (Typha species), which grow in wetlands and swamps across the continent. Cattails are named for the thick brown flower spikes which grow above the tall, strap-like leaves.
The American lotus (Nelumbo lutea) is a showier emersed native plant. Similar to a water lily, the lotus' round leaf usually stands completely out of the water, sometimes resting on the surface. The striking pale yellow flowers grow to 6 inches or more across and are distinctive for the flat-topped seed head that protrudes from the middle.
Duck potato (Sagittaria lancifolia) is another common American aquatic plant, growing in ponds, along stream banks and in ditches. The plant's defining characteristics are its 2-foot-tall, Romaine lettuce-like leaves. The plant bears tall stalks of three-petaled white flowers with green or yellow centers.
Native Floating-Leaf Plants
The native water lily (Nymphaea odorata) is the most distinctive of North America's floating-leaf plants. Anchored into the mud at the bottom of still waters, the water lily's round leaves rest directly on the water's surface and are cut along one side. The white, fragrant flowers open in the morning hours and close in the afternoon.
Noxious Non-Native Aquatic Invasives
Several introduced aquatic plant species have earned themselves reputations as thugs for their rapid and rampant spread. Though beautiful, these plants are banned in many states because they frequently escape into naturalized settings, quickly crowding out the native plants upon which many animal species rely for food and shelter.
The federal government first instituted measures against the water hyacinth (Eichhornia crassipes) over 100 years ago, though it still crowds waterways, lakes and ponds across the country today. Water hyacinth leaves are usually round with a leathery appearance, attached at the base to a fleshy floating bulb. The stalk of showy lavender flowers that appear from June to September was one of the original reasons the plant was introduced.
Hydrilla (Hydrilla verticillata) is a submersed plant that looks very similar to the native elodea but differs through the presence of tooth-like ridges along the underside of the leaves. Plant branches are covered with whorls of blade-like leaves every one-fourth to one-half inch along the stem. Hydrilla can grow from depths of up to 20 feet to reach the water's surface, where it grows to form dense mats that prevent sunlight from penetrating the water.