Family: Haloragaceae (Water-Milfoil Family)
Duration and Habit: Perennial Submerged aquatic
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Like many milfoils, Eurasian watermilfoil is a submersed perennial plant with finely dissected feather-like leaves and thin stems. The leaves are arranged in whorls of 4 (rarely 5) around the stem at each node. Each Eurasian watermilfoil leaf generally has 14 or more leaflet pairs and this feature can be used most of the time to distinguish Eurasian watermilfoil from other milfoil species that have whorls of 4 leaves but fewer than 14 leaflet pairs. However, the number of pairs of leaf divisions is highly variable, with younger plants and growing fragments often having fewer than 14. The tips of Eurasian watermilfoil that emerge from the water are often red—especially early in the growing season—
and these reddish spikes stand several inches above the water and submerge when pollination is complete. Flowers are tiny and pink; lower flowers are pistillate and upper flowers are staminate. Seeds are produced, but seedlings are rare in nature.
In situations where water evaporates slowly, and the plants gradually become stranded, Eurasian watermilfoil can develop into a land form. The leaves of the land form are smaller, stiffer, and have fewer divisions. If such plants are submerged, new growth with aquatic leaves develops in 7-10 days, but the first leaves formed have relatively few divisions and only later does the number of divisions increase to more than 12 leaflet pairs.
Native Lookalikes: Eurasian watermilfoil most closely resembles native milfoil species but can be distinguished by comparison of the number of leaflet pairs in most cases as well as the emergent tips. Native watermilfoils with whorls of 4 leaves have fewer than 14 leaflet pairs and Eurasian watermilfoil typically has 14 or more. The emergent tips of the native species have fleshy, succulent-like leaves whereas the emergent tips of Eurasian watermilfoil lack leaves and have small flowers and, later, fruits.
Whorled watermilfoil (Myriophyllum verticillatum)
The best way to identify whorled water milfoil is by looking at its two different types of leaves, submersed and emergent. Submersed leaves look feathery and possess about 5 to 14 leaflet pairs per leaf—Eurasian watermilfoil leaves have typically more than 14. They are arranged on the stem in whorls of typically 4 to 5 leaves, which are spaced about 1 cm apart. Emergent leaves occur on the emergent flowering stem and are pinnately lobed. Eurasian milfoil lacks emergent leaves.
Another way to distinguish whorled water milfoil is to look for turions, winter buds that appear toward the end of its growing season. The turions of this milfoil look like long yellowish-green club-shaped buds with small stiff leaves attached to the submerged stem. This milfoil is one of a few that produce turions. This characteristic rules out other types of watermilfoil that lack turions, including Eurasian watermilfoil. If you see turions or the turion leaves, you DO NOT have Eurasian watermilfoil.
Twoleaf watermilfoil (Myriophyllum heterophyllum)
The leaves of twoleaf water milfoil possess about 5 to 10 leaflet pairs per leaf—Eurasian watermilfoil leaves have typically more than 14. The emergent stems of this milfoil also possess leaves, which, again, Eurasian milfoil does not. The photo illustrates the common name: the feathery submersed leaves and the simple, more robust leaves of the emergent flowering stem.
Ecological Threat: Eurasian milfoil can form large, floating mats of vegetation on the surface of lakes, rivers, and other water bodies, preventing light penetration for native aquatic plants and impeding water traffic. The plant thrives in areas that have been subjected to various kinds of natural and manmade disturbance.
Biology & Spread: Relative to other submersed plants, Eurasian watermilfoil requires high light, has a high photosynthetic rate, and can grow over a broad temperature range. Most regeneration of Eurasian watermilfoil is from rhizomes, fragmented stems, and axillary buds that develop throughout the year. Flower spikes (i.e., emergent tips) often remain above water until pollination is complete, then resubmerge. Although seeds are usually viable, they are not an important means of dispersal. It appears to be primarily spread from waterbody to waterbody through boating activity although anglers have been known to deliberately plant this species in lakes.
History: Eurasian watermilfoil may have been introduced to the North American continent at Chesapeake Bay in the early 1880s, although Couch and Nelson present evidence that the first collection of Eurasian watermilfoil was made from a pond in the District of Columbia during the fall of 1942. By 1985, this invasive plant had been found in 33 states, the District of Columbia, and the Canadian provinces of British Columbia, Ontario, and Quebec. Eurasian watermilfoil was first documented in Texas in 1962.
U.S. Habitat: Eurasian watermilfoil is an extremely adaptable plant, able to tolerate and even thrive in a variety of Eurasian watermilfoil is an extremely adaptable plant, able to tolerate and even thrive in a variety of environmental conditions. It grows in still to flowing waters, can tolerate salinities of up to 15 parts per thousand, grows rooted in water depths from 1 to 10 meters (regularly reaching the surface while growing in water 3 to 5 meters deep), and can survive under ice. It can tolerate a range of pH from 5.4-11. Eurasian watermilfoil grows best on fine-textured, inorganic sediments and relatively poorly on highly organic sediments. conditions. It grows in still to flowing waters, can tolerate salinities of up to 15 parts per thousand (half the salinity of Puget Sound), grows rooted in water depths from 1 to 10 meters (regularly reaching the surface while growing in water 3 to 5 meters deep), and can survive under ice. It is able to tolerate pHs from 5.4-11. Relative to other submersed plants, Eurasian watermilfoil requires high light, has a high photosynthetic rate, and can grow over a broad temperature range. Eurasian watermilfoil grows best on fine-textured, inorganic sediments and relatively poorly on highly organic sediments.
U.S. Nativity: Introduced to U.S.
Native Origin: Europe, Asia, northern Africa
U.S. Present: AL, AZ, AR, CA, CO, CT, DE, DC, FL, GA, ID, IL, IN, IA, KS, KY, LA, ME, MD, MA, MI, MN, MS, MO, MT, NE, NV, NH, NJ, NM, NY, NC, ND, OH, OK, OR, PA, RI, SC, SD, TN, TX, UT, VT, VA, WA, WV, WI.
Distribution: Eurasian watermilfoil is found across the U.S. and several Canadian provinces and is especially widely distributed across the northeast from Wisconsin to Vermont and Massachusetts.
List All Observations of Myriophyllum spicatum reported by Citizen Scientists
Yellow nelumbo (Nelumbo lutea), pond weed (Potamogeton nodosus), butterweed (Senecio glabellus) are some alternative plants to consider for the eastern U.S.
White water lily (Nymphaea odorata), Floating bladderwort (Utricularia radiata), American eelgrass (Vallisneria americana) in Texas. Native Texas alternatives include
Physical removal of Eurasian watermilfoil can be effective in small areas such as boat slips but treatments with herbicides are necessary to control extensive infestations. Care should be taken during physical removal; fragmentation promotes spread. Because Eurasian watermilfoil is prohibited in Texas, a permit may be required for physical removal. A nuisance aquatic vegetation treatment proposal is required for chemical, physical, or biological control of any aquatic plant species on a public water body. Water level control is also effective.USE PESTICIDES WISELY: ALWAYS READ THE ENTIRE PESTICIDE LABEL CAREFULLY, FOLLOW ALL MIXING AND APPLICATION INSTRUCTIONS AND WEAR ALL RECOMMENDED PERSONAL PROTECTIVE GEAR AND CLOTHING. CONTACT YOUR STATE DEPARTMENT OF AGRICULTURE FOR ANY ADDITIONAL PESTICIDE USE REQUIREMENTS, RESTRICTIONS OR RECOMMENDATIONS. MENTION OF PESTICIDE PRODUCTS ON THIS WEB SITE DOES NOT CONSTITUTE ENDORSEMENT OF ANY MATERIAL.
B.C. Ministry of Environment 1989. Eurasian Water Milfoil in British Columbia (Pamphlet).
Gleason, H.A., A. Cronquist. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. 2nd ed. The New York Botanical Garden, 910.
APWG WeedUS Database
Entry in iNaturalist.
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