Aquatic invasive species

General Information

Fragrant water lilies (Nymphaea odorata) are exceptionally beautiful water plants with floating leaves and large many-petaled fragrant blossoms. They are wonderful additions to backyard ponds and even "tub gardens." The nursery industry has hybridized them and produced many color variations. They sell tropical water lilies and hardy water lilies. It is the hardy white and (sometimes) pink lilies that have become naturalized in Washington lakes and rivers. These plants are native to the eastern United States and it is believed that the water lily was introduced to Washington during the Alaska Pacific Yukon Exposition held in Seattle in the late 1800s. Because of their great beauty, water lilies have been intentionally planted in many Washington lakes, especially those lakes in western Washington. However, lake residents are strongly discouraged from planting fragrant water lilies in lakes or natural waterbodies. Not only are water lilies aggressive plants, but sometimes "hitchhiker" plants such as hydrilla can also be introduced to our lakes when water lilies are planted.

Growth Habit

Water lilies grow in dense patches, excluding native species and even creating stagnant areas with low oxygen levels underneath the floating mats. These mats make it difficult to fish, water ski, swim, or even paddle a canoe through. Although relatively slow-spreading, water lilies will eventually colonize shallow water depths to six feet deep and can dominate the shorelines of shallow lakes. For this reason, planting water lilies in lakes is not recommended. Water lilies reproduce by seed and also by new plants sprouting from the large spreading roots (underground stems called rhizomes). A planted rhizome will cover about a 15-foot diameter in about five years.

Fragrant water lily has an interesting pollination strategy. Each white or pink flower has many petals surrounding both male and female reproductive parts, and is only open during the daytime for three days. On the first morning, the flowers produce a fluid in the cup-like center and are receptive to pollen from other flowers. However, they are not yet releasing pollen themselves. Pollen-covered insects are attracted by the sweet smell, but the flower is designed so that when they enter the flower, they fall into the fluid. This washes the pollen off their bodies and onto the female flower parts (stigmas) causing fertilization. Usually the insects manage to crawl out of the fluid and live to visit other flowers, but occasionally the unfortunate creature will remain trapped and die when the flower closes during the afternoon. On the second and the third days, the flowers are no longer receptive to pollen, and no fluid is produced. Instead, pollen is released from the stamens (the flexible yellow match-shaped structures in the flower center). Visiting insects pick up the pollen and transport it to flowers in the first day of the flowering cycle. After the three days the flowers are brought under water by coiling their stalks. The seeds mature under water and after several weeks are released into the water. Water currents or ducks, which eat the seeds, distribute them to other areas. This flowering regimen is followed nearly throughout the summer, producing many eye-pleasing blooms and a large supply of seeds.

In addition to reproducing by seeds, water lilies spread by rhizomes. Anyone who has tried to curtail this plant's growth in front of their dock knows how tenacious these root systems are. Also, if pieces of the rhizome are broken off during control efforts, they will drift to other locations and establish a new patch of lilies.

Native American Use

The fragrant water lily was utilized in many ways by Native Americans in the eastern United States. Roots of this and other water lilies were used medicinally as a poultice for sores and tumors, internally for many aliments including digestive problems, and rinse made for sores in the mouth. The leaves and flowers were also used as cooling compresses. In addition, the rhizomes were occasionally used as food and the young leaves and lower buds were eaten as a vegetable. Even the seeds were fried and eaten or ground into flour. Wildlife, including beaver, muskrat, ducks, porcupine, and deer also will eat the leaves, roots, or seeds. In moderate quantities the fragrant water lily can also benefit the lake by providing shelter and habitat for fish and invertebrates and shade to cool the water. However, our native water lilies, like spatterdock (Nuphar polysepalum) and watershield (Brasenia schreberi), will also provide the same benefits as the fragrant water lily and are not invasive.

Identification

Because of their large, showy flowers, water lilies are easy to identify when flowering. They have white or pink showy flowers. When not in flower look for:

Nearly-circular floating leaves, up-to-11 inches in diameter.

The underside of the leaf is often red or purple with numerous veins.

The stem is attached to the center of the leaf.

The leaves each have a deep cleft to the stem.

General Information

Eurasian watermilfoil (Myriophyllum spicatum) is an attractive plant with feathery underwater foliage. It was once commonly sold as an aquarium plant. Eurasian watermilfoil, hereafter called milfoil, originates from Europe and Asia, but was introduced to North America many years ago and is now found over much of the United States. This plant was introduced to the eastern United States at least as long ago as the 1940s, but it may have arrived as early as the late 1800s. The first known herbarium specimen of milfoil in Washington was collected from Lake Meridian near Seattle in 1965. By the mid 1970s it was also found in Lake Washington. During this same time period milfoil became established in central British Columbia and traveled downstream to Lake Osoyoos and the Okanogan River in central Washington. Now milfoil is found in the Columbia, Okanogan, Snake, and Pend Oreille Rivers and in many nearby lakes. In western Washington, the distribution of milfoil closely follows the Interstate 5 corridor. It is very apparent that milfoil has been spread from lake to lake on boat trailers.

Growth Habit

Because it is widely distributed and difficult to control, milfoil is considered to be the most problematic plant in Washington. The introduction of milfoil can drastically alter a water body's ecology. Milfoil forms very dense mats of vegetation on the surface of the water. These mats interfere with recreational activities such as swimming, fishing, water skiing, and boating. In eastern Washington milfoil interferes with power generation and irrigation by clogging water intakes. The sheer mass of plants can cause flooding and the stagnant mats can create good habitat for mosquitoes. Milfoil mats can rob oxygen from the water by preventing the wind from mixing the oxygenated surface waters to deeper water. The dense mats of vegetation can also increase the sedimentation rate by trapping sediments.

Milfoil also starts spring growth sooner than native aquatic plants and can shade out these beneficial plants. When milfoil invades new territory, typically the species diversity of aquatic plants declines. While some species of waterfowl will eat milfoil, it is not considered to be a good food source. Milfoil reproduces extremely rapidly and can infest an entire lake within two years of introduction to the system. Although milfoil produces many seeds, we do not believe that these seeds are important for milfoil reproduction in Washington waters. However, milfoil is able to reproduce very successfully and rapidly through the formation of plant fragments. In the late summer and fall the plants become brittle and naturally break apart. These fragments will float to other areas, sink, and start new plants. Milfoil will also grow from fragments created by boaters or other disturbances during any time of year. A new plant can start from a tiny piece of a milfoil plant. This is why milfoil can so easily be transported from lake to lake on boat trailers or fishing gear. Once established in its new home, water currents may carry milfoil fragments and start new colonies within the same waterbody.

Identification

The genus is easy to identify because all milfoils have feather-like leaves arranged in whorls around the stem. Identifying individual species is much more difficult and even the plant experts rely on DNA analysis to tell some species from each other. There are several native milfoil species in Washington and some species like northern milfoil (Myriophyllum sibericum) are commonly found in Washington lakes. In fact, for many years northern milfoil and Eurasian water milfoil were classified as the same species. Currently botanists seem to be in agreement that the two are separate species, though often can look very similar. Unfortunately not all northern and Eurasian milfoil leaflets look so differently from each other. Sometimes these two species look very similar and when that happens it is best to rely on DNA or pigment analysis for positive identification.

Here are some tips to identify Eurasian watermilfoil from the native milfoils.

Count the pairs of leaflets. Eurasian watermilfoil usually has twelve or more pairs on each leaf.
Eurasian watermilfoil leaves tend to collapse around the stem when removed from the water. Other milfoil species have thicker stems and are usually more robust.
The mature leaves are typically arranged in whorls of four around the stem.
Contact Jenifer Parsons, Ecology's botanist, at Jenifer.Parsons@ecy.wa.gov for positive identification.

(Used with Permission from the Washington State Department of Ecology)