Descriptions of the following aquatic plant species are provided by this page.

	Myriophyllum spicatum (Eurasian Watermilfoil)
	Lytbrum salicaria (Purple Loosestrife)
	Hydrilla verticillata (Hydrilla)
	Phalaris arundinacea (reed canary grass)
	Iris pseudacorus (yellow iris)
	Nympbaea odorata (white/pink waterlily)

 

Myriophyllum spicatum (Eurasian Watermilfoil)

Myriophyllum spicatum is an invasive submergent non-native plant and can be found in water depths ranging from several feet to 15 feet. The leaves of M. spicatum are distinctly feather-like in appearance with twelve or more leaflet pairs along the main vein of the leaf. The leaflets are arranged in whorls of four along the plant stem. The lower portion of the plant is dominated mostly by the stem in deeper waters with leaf whorls spacing becoming closer at the top of the plant. As the plant reaches the water surface, it continues to grow prostrate, forming thick dense mats impeding boating, fishing, and swimming activities. The plant easily regrows from small fragments which are spread throughout the lake from boating, fishing, hand-removal, mechanical harvesting, and wave action.

Most accounts suggest that M spicatum was first introduced into Washington in the mid-1970s. However, the University of Washington has a herbarium specimen from Lake Meridian (Kent, Washington) which documents its presence in King County as early as 1965 (J. Parson, personal communication, August 1996).

Lytbrum salicaria (Purple Loosestrife)

Lythrum salicaria is a tall perennial herb with multiple stems which originate from a woody root system. The stems are characteristically square in cross section. The lance shape leaves are typically opposite but occasionally can be found in whorls of three or alternately along the plant stem. The bright magenta flowers on a terminal spike are one of the most distinguishing features of this herb.

The plant is very invasive and can take over a shoreline or wetland area in just a few years since mature plants generally produce a million or more viable seeds each year. The plant also reproduces vegetatively from the root stock and from stem fragments, which further hinders successful removal. The tiny seeds have little food value and the thick plant stands deter wildlife use for nesting or cover.

L. salicaria was first introduced into North America during the 1800s. The plant quickly spread throughout the east and Great Lakes states after its introduction and eventually found its way west. The plant was first documented in Washington during the 1920s. Limited historical information on L. salicaria presence is available in the King County wetlands inventory.

L. salicaria was found in 12 of the 36 lakes surveyed. The level of infestation varied from lake to lake ranging from just a few plants (Pine Lake) to extensive shoreline coverage (Lake Desire). For many of the lakes with small plant populations, hand pulling methods combined with ongoing surveying could be used to eradicate L. salicaria from the shoreline.

Hydrilla verticillata (Hydrilla)

Hydrilla verticillata closely resembles both Egeria densa and Elodea candensis which are found in Washington. H verticillata is readily distinguished by the presence of small, peanut-sized tubers found at the end of underground rhizomes. The leaves can be found along the plant stem in whorls of three-eight and can be distinguished by their serrated edges.

H. verticillata had not been identified in Washington until its discovery in lakes Lucerne and Pipe during the SWM Division surveys. Since the discovery of H verticillata in these King County lakes, the SWM Division, with the assistance of the Washington Department of Ecology (and an Aquatic Weed Management Fund grant), has completed the second year of management efforts to eradicate the plant from the lakes.

Phalaris arundinacea (reed canary grass)

This perennial grass grows between three and five feet tall from spreading underground rhizomes. The plant was originally introduced as forage for cattle and is commonly found invading wet open areas which have been disturbed. The grass is ideally suited to highly fluctuating water tables which are common to lake shorelines. The plant provides little habitat for waterfowl and wildlife because of its dense growth. Few species, other than cattle, enjoy it as a food source. Lakes Beaver and Twelve were the only shorelines where this species was observed.

Iris pseudacorus (yellow iris)

This non-native emergent plant grows from underground rhizomes to a height of three feet. The showy yellow flowers make the plant rather attractive. However, like most noxious species, the non-native iris replace more beneficial species including cattails, sedges, rushes, and other native shoreline vegetation. The yellow iris was found on 32 of the 36 surveyed lakes. This species was frequently observed along residential portions of the shoreline which had been altered or disturbed in some fashion. In many of the surveyed lakes, the plant was well established and was continuing to spread to other disturbed sites.

Nympbaea odorata (white/pink waterlily)

The white or pink fragrant waterlilies are probably the most easily recognized aquatic plant species. The large floating leaves are nearly round and are generally between six and 12 inches in diameter. The flowers are white or pink with many petals. This plant was introduced to many King County lakes as a horticultural specimen by lakeside residents and was found on 27 of the 36 surveyed lakes. The plant can become a problem in shallow embayments, restricting access to open water areas of a lake. Although residents were well intentioned with this plant introduction, this species is now the target of most aquatic plant management complaints. The plant is difficult to remove because of its large underground tuber which continues to send up new shoots throughout the growing season.