Rivers of Illinois: Mississippi, Illinois, Wabash and Ohio Ecology: Plants Ecology is the scientific study of relations that organisms have with respect to each other and their natural environment. In this podcast we will focus on plants, those in the rivers as well as in the lands around them. Within the rivers, there are four types of aquatic vegetation: algae; floating plants; submersed plants; and emersed plants. Algae Algae are small, primitive plants that do not have true leaves or flowers. In rivers, they generally can be found attached to submerged objects. Algae grow in several forms. Filamentous algae are composed of clumps of long, hairlike strands that may appear slimy or cottony. Another group of algae includes the species in the genus Chara. These algal species have bristly stems and branches. Chara species tend to grow in backwater lakes and slow-moving streams that connect to the rivers. Floating Plants Floating plants are not attached to anything and float freely on the surface of the water. Duckweed is a floating plant with tiny leaves and rootlets that hang in the water. It often grows with water meal, the smallest flowering plant. Water meal looks like minute green grains floating on the water. These plants tend to accumulate in layers on the water and drift with the wind and currents. In large rivers, they are only found in areas of low current or in backwater lakes. Submersed Plants Submersed plants are usually rooted in the bottom of the water body. They have stems and leaves that grow to or close to the water’s surface. Because of the strong currents in these large rivers, many submersed plants cannot grow here. Leafy pondweed is an example of a submersed plant species. Emersed Plants Emersed plants grow above the water in shallow areas along the shoreline. Common arrowhead plants are also called duck potato plants because of their tuberlike roots that are a favorite food of waterfowl. Their leaves are shaped like arrowheads, and they produce tiny white flowers. Creeping primrose willow has hollow red stems that extend from the shoreline. Beneath each stem is an extensive fine root system below the water. In the summer this species produces bright yellow flowers. Knotweed has jointed stems. In the summer it produces dense clusters of pink or rose-colored flowers. Near the Rivers Many plant species grow in the wet soils along the large rivers. Common cat-tail is a plant with long, flat leaves. It usually produces an elongated stalk with a seed spike at the end, making it look like a cat’s tail. Buttonbush is a shrub with opposite leaves or leaves in groups of three. It is called “buttonbush” because of the round clusters of flowers that develop on long stalks. The river birch tree can be 75 feet tall. It has red-brown bark that peels off in papery shreds. The leaves are sharply toothed and taper at the base. Eastern cottonwood trees can grow to 100 feet tall. When they are young the bark is smooth and gray, and as they age it becomes furrowed. The leaves are triangular in shape, and the seeds have cottony fibers attached to them to help with wind dispersal. Sandbar willows are much shorter, only reaching 25 feet tall. These trees have long, narrow leaves with widely spaced teeth. The bark is gray, furrowed and broken into rough scales. Silver maple can grow to 100 feet tall. The underside of the leaf has a silvery appearance, and each leaf has five deep lobes that are each toothed and pointed at the tip. Sycamore trees have red-brown bark that breaks into thin, flat scales as the tree grows. The bark falls away in sections exposing the white or green inner bark. The bottomland forests of the Wabash River once contained sycamores that were the largest trees east of the Rocky Mountains. Invasive Species An invasive species is one that is not native to an ecosystem and whose introduction causes environmental harm. Invasive exotic plants can out-compete native vegetation and dominate the habitat, causing many problems in natural food chains and webs. Purple loosestrife is a severe threat to native emersed vegetation. This erect, herbaceous plant has red-purple flower spikes and produces millions of seeds every year, allowing it to spread rapidly. Common reed is an invasive species that consumes available growing space and pushes out other plants. This grass has stems that can grow up to 15 feet tall. It has dark blue-green leaves and lives near river edges in full sunlight. Reed canary grass takes over wetland areas and river banks. Although it looks similar to native grasses, it is distinctively transparent where the leaf blade meets the stem. It is used for feeding grazing livestock and to help control erosion in agricultural areas, but it can escape and form dense colonies that exclude other plants and change animal habitat. Endangered and Threatened Species Endangered species are those plants and animals that have become so rare they are in danger of becoming extinct. Threatened species are those plants and animals that are likely to become endangered within the foreseeable future. Species can disappear due to changes caused by nature or by human actions. Natural disasters, pollution and the introduction of new species to an area are all major causes of disappearing species. The rivers in Illinois have several endangered and threatened species. The decurrent false aster is considered an Illinois and federally threatened plant. It grows in alluvial prairies, areas where flowing water has left many nutrients in the soil, and marshlands of the Illinois River and near the Mississippi River close to St. Louis. It is threatened due to destruction and modification of its floodplain habitat due to agricultural expansion, flood control and erosion. Its seeds are sensitive to pollution and unlikely to germinate if the water is polluted. Lea’s bog lichen is found on tree trunks below the spring high water mark. It is threatened mostly because of the levees, locks and dams that prevent many areas around the rivers from flooding naturally. The water willow species is endangered in Illinois. It grows in the southern tip of the state in swamps and floodplain forests. Another species in these extreme southern floodplains is willow oak. These trees can grow to be over 80 feet tall and are threatened in Illinois. Some plants thrive in the moist areas near the rivers while others live directly in the water. The large rivers of Illinois support a great variety of plants, from tiny algae to huge, towering trees.