Aquatic Plant Identification

Successful treatment of nuisance aquatic plants begins with accurate identification of the offending plant. There are dozens of aquatic plant and algae species that occur in Pennsylvania. Some are unique and easy to identify while others look very inconspicuous. Aquatic plants can be separated into four categories. Algae are the most common type of aquatic plant and the most common to grow to a nuisance level. Planktonic algae are minute single-sellled plants that are suspended in the water, giving the pond a pea soup green, reddish, or brown appearance. Filamentous forms of algae begin to grow on the bottom of the pond in shallow water, then break loose and float to the top in large mats. A few less common forms of algae can even look like rooted plants. The most diverse group of aquatic plants are the submerged plants that are usually rooted to the bottom and have submerged leaves and stems. Most grow in shallow water less than 4 ft deep where sunlight penetrates to the bottom of the pond. Some submerged plants are annuals that die each year and regrow by seeds the following year, but most rely on continual spreading growth from ryomes or roots. A few even remain green all year long. Most native submerged plants are beneficial to the pond, providing important underwater habitat and only rarely reach nuisance levels. Some of the most common native submerged plants are elodia, niad, and leafy pondweed. But there are several non-native submerged plants that often grow to nuisance levels and are increasingly being found in ponds in Pennsylvania. Curly leaf pondweed is one of the most common invasive submerged plants. It has a very distinctive appearance with crinkled, finely tothed leaves that occur alternately along the stem. Hydrillaa is another invasive submerged plant that is currently most common in southern Pennsylvania ponds. It has dense, finely tothed leaves coming off stems in whs of 3 to eight. Finally, Eurasian mil foil is an invasive non-native plant that quickly grows to nuisance levels. The leaves are dark green or reddish in color with a fine feather-like appearance, growing on long, thin stems. Floating aquatic plants have most or all of their leaves floating freely on the pond surface. Some common floating plants are actually rooted on the bottom like water lily, spatter dock, Two smaller floating aquatic plants have become a major nuisance for many pond owners. Duckweed with its small free floating leaves can spread rapidly across the pond surface, especially if the water is stagnant. Watermeal, which also likes stagnant water, looks very much like bright green grass seed and feels gritty when rubbed between your fingers. Both of these plants are frequently spread between ponds on the feathers and feet of geese and ducks. The final group of aquatic plants are emergent varieties that grow around the edge of the pond arrowheads, and bull rush. They like to have their roots in wet sediment, but their stems and leaves above the water surface. Most emergent plants grow slowly and provide excellent fish and wildlife habitat. Emergent plants tend to cause few problems for pond owners with the exception of a few non-native invasive species like purple loose stripe. This non-native plant was imported from Europe and Asia and is quickly spread throughout the state. It easily outco competes native emerging plants and should be removed as soon as it first appears. You can get help in identifying your pond plants by visiting the Penn State Pond website or by emailing a digital photo of the plant to the email address