Eurasian watermilfoil is a submerged invasive aquatic plant native to Asia, Europe and Africa in the Haloragaceae family. It typically grows in water 3.2 to 13 feet deep, tolerates cold waters and low light conditions, and has spread to nearly every state in the USA and much of Canada. It was likely first brought to North America in ship ballasts or as an ornamental plant for aquariums or water gardens. Once introduced to an aquatic system, it spreads prolifically by stem fragments caused by either natural or mechanical causes. Each plant produces around 100 seeds but the main propagation method for this plant is stem fragments. This plant interferes with the recreational uses of waterways, obstructs commercial navigation, exacerbates flooding, clogs hydropower turbines and alters ecosystems by crowding out native plants and affecting animal diversity. It will also hybridize with native watermilfoil species making control more difficult. The stems of this plant can grow up to 20 feet long with feathery whorled leaves around the stem. The plant has separate male and female flowers in summer. A 2-6 inch spike is produced with inconspicuous small reddish or pinkish 4-petaled flowers and is held above the water. until flowering is complete, then becomes parallel with the water. Insects, Diseases, and Other Plant Problems: No significant problems. On the NC noxious weed list, this species is considered invasive by the NC Invasive Plant Council and in many other states. It is illegal to sell this plant in many states.
Curated pairwise relationships between this plant and others in the library — who feeds
whom, who competes, who confuses the pests. Green reads as a good pairing, red as one to avoid.
No curated interactions recorded for this species yet.
Also noted by NC State
Related species the NC State Plant Toolbox flags for this plant — look-alikes to tell
apart, and plants that play a similar role in a planting. Ones we carry in the library are linked.
Dappled Sunlight (Shade through upper canopy all day) | Deep shade (Less than 2 hours to no direct sunlight) | Full sun (6 or more hours of direct sunlight a day) | Partial Shade (Direct sunlight only part of the day, 2-6 hours)
Soil drainage
Frequent Standing Water
NC region
Coastal; Mountains; Piedmont
Growth rate
Rapid
Maintenance
High
Form & Appearance
Habit / form
Spreading
Texture
Medium
Leaf color
Green
Leaf type
Compound (Pinnately , Bipinnately, Palmately)
Leaf arrangement
Whorled
Leaf shape
Filiform
Leaf feel
Soft
Leaf size
1-3 inches long, < 1 inch wide
Hairs present
No
Leaf detail
The submerged olive-green leaves are less than 2 inches long and borne in pinnate whorls of four, with numerous (14-24) thread-like leaflets (filiform) roughly 4–13 mm long.
Flower color
Gold/Yellow; Pink; Red/Burgundy
Flower form
Insignificant; Spike
Flower detail
Plants are monoecious with both male and female flowers produced in the leaf axils. Each inconspicuous flower is orange-red to pinkish to yellow, 4–6 mm long, on a 2-8 inch spike held erect above the water. The 4-petaled flowers are in whorls along the spike with 4 sepals and 8 stamens. Usually flowers twice a year in mid-June and late-July
Bloom time
Summer
Fruit type
Capsule
Fruit size
< 1 inch long, < 1 inch wide
Fruit detail
4-lobed capsule splitting into 4 nutlets.
Stem color
Brown/Copper; Pink; Red/Burgundy; White
Stem detail
Stems slender, smooth, 6 to 20 ft. long, reddish-brown to whitish-pink; branching several times near the water surface.