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Spike Watermilfoil Myriophyllum spicatum

Other Common Name(s):

Previously known as:

  • Myriophyllum verticillatum subsp. spicatum
This plant is an invasive species in North Carolina
Description

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.

See this plant in the following landscape:
Cultivars / Varieties:
Tags:
#invasive#high maintenance#fast growing#aggressive#spreading#Noxious Weed List#weed#waterweed#aquatic weed#submerged
 
Cultivars / Varieties:
Tags:
#invasive#high maintenance#fast growing#aggressive#spreading#Noxious Weed List#weed#waterweed#aquatic weed#submerged
  • Attributes:
    Genus:
    Myriophyllum
    Species:
    spicatum
    Family:
    Haloragaceae
    Life Cycle:
    Perennial
    Country Or Region Of Origin:
    Europe, Asia, Africa
  • Whole Plant Traits:
    Plant Type:
    Water Plant
    Weed
    Habit/Form:
    Spreading
    Growth Rate:
    Rapid
    Maintenance:
    High
    Texture:
    Medium
  • Cultural Conditions:
    Light:
    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
    USDA Plant Hardiness Zone:
    3a, 3b, 4a, 4b, 5a, 5b, 6a, 6b, 7a, 7b, 8a, 8b, 9a, 9b, 10a, 10b
  • Fruit:
    Fruit Type:
    Capsule
    Fruit Length:
    < 1 inch
    Fruit Width:
    < 1 inch
    Fruit Description:
    4-lobed capsule splitting into 4 nutlets.
  • Flowers:
    Flower Color:
    Gold/Yellow
    Pink
    Red/Burgundy
    Flower Inflorescence:
    Insignificant
    Spike
    Flower Bloom Time:
    Summer
    Flower Petals:
    4-5 petals/rays
    Flower Description:
    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
  • Leaves:
    Leaf Color:
    Green
    Leaf Feel:
    Soft
    Leaf Type:
    Compound (Pinnately , Bipinnately, Palmately)
    Leaf Arrangement:
    Whorled
    Leaf Shape:
    Filiform
    Hairs Present:
    No
    Leaf Length:
    1-3 inches
    Leaf Width:
    < 1 inch
    Leaf Description:
    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.
  • Stem:
    Stem Color:
    Brown/Copper
    Pink
    Red/Burgundy
    White
    Stem Is Aromatic:
    No
    Stem Surface:
    Smooth (glabrous)
    Stem Description:
    Stems slender, smooth, 6 to 20 ft. long, reddish-brown to whitish-pink; branching several times near the water surface.
  • Landscape:
    Resistance To Challenges:
    Wet Soil
    Problems:
    Invasive Species
    Weedy