The Biology of Aquatic Vascular Plants

Free-floating

• Biologists define free-floating aquatic plants as those that float on the surface of the water. Their most notable adaptation is their limited root structure, and because of it, they usually grow in very still, protected water sources. Some examples of free-floating aquatics are duckweed (Lemna spp.), bladderwort (Utricularia vulgaris) and coontail (Ceratophyllum demersum).

Submergent

• The one defining characteristic of submergent aquatic plants is that they have roots or rhizomes (underground stems) that anchor them to the floor of the body of water where they live. They often have thin, trailing leave, which may be floating or completely covered in water. The leaves of these plants have adapted to be very flexible, so they can move along with currents and winds without damage. Additionally, their tissue structures differ from terrestrial plants since they are lighter and sometimes contain pockets of air. Submergent plants appear in both very shallow and very deep waters. Common examples include pondweed (Potamogeton spp.), water milfoil (Myriophyllum spp.), waterweed (Elodea spp.) and widgeon grass (Ruppia maritima).

Emergent

• Emergent aquatic plants grow in saturated soils. While their stems may be covered in water, their leaves always grow above the surface. They typically appear in wetland areas or on the edges of larger bodies of water, and prefer areas where the water depth measures 4 to 5 feet. Many of these types of aquatic plants look very similar to grasses. Some examples are arrowhead (Sagittaria spp.), cattail (Typha spp.), common reed (Phragmites australis), and bulrush (Scirpus spp.).

Amphibious

• Amphibious plants may grow either completely submerged in water or as emergent plants. They are very hearty because they can survive dropping water levels and live as terrestrial plants when necessary. Usually, the growth that occurs during these periods has a very different appearance from that which occurs when submerged. Many of these plants are extremely sensitive to the changes in CO2, light and oxygen levels that accompany a dip in water depth, and these variations can change their physiology accordingly. Examples include yellow water-crowfoot (Ranunculus flabellaris), pepperwort (Lepidium ruderale) and water smartweed (Polygonum amphibium).