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Similar but less problematic plants:
Iris versicolor Flower detail
Hydrilla verticillata is often confused with:
Elodea densa Form blooming in water
Native alternative(s) for Hydrilla verticillata:
Azolla caroliniana Fronds (Niagara-on-the-Lake, ON)-Early Fall
Bacopa caroliniana Flowers
Iris virginica Iris virginica
Nymphoides cordata Form in bloom
Pontederia cordata Pontederia cordata
Plants that fill a similar niche:
Ludwigia hexapetala Form in flower
Murdannia keisak Flower detail
Myriophyllum spicatum Form in water

Waterthyme Hydrilla verticillata

Other Common Name(s):

Previously known as:

  • Elodea verticillata
Phonetic Spelling
hy-DRIL-lah ver-TIS-sil-la-tah
This plant is an invasive species in North Carolina
Description

Waterthyme is an invasive rooted aquatic plant in the Hydrocharitaceae family and is native to  Asia, Africa and Australia. It is the only species in the genus but many consider it to have several variations. It was introduced through the aquarium trade and was subsequently dumped into the waterways. It can now be found from Connecticut south to Florida, into the central USA, west to Texas and up the Pacific coast. It is found throughout NC in various freshwater systems.

It is considered one of the worse invasive plants in this country and the world and is on the USDA Noxious Weed List. It is listed as invasive by the NC Invasive Plant Council and many other states.

The stems are slender and branched, up to 25’ long. The leaves are in bottle-brush whorls of 3-8 with serrated margins, reddish midribs and undersides with small sharp teeth. Tiny white flowers have 6 petals and grow on long stalks. There are both monoecious (both male and female flowers on the same plant) and dioecious (male and female flowers on different plants) forms. The plants are spread both by seeds and vegetatively. They overwinter in colder climates by their tubers.

In addition to forming large monoculture mats that crowd out native plants and alter the ecosystem, the plant harbors bacteria that cause a brain-wasting disease in waterfowl. It is very versatile and can grow in almost any freshwater system including springs, lakes, marshes, ditches, rivers and tidal zones in water a few inches and up to 20 feet deep. It can grow sun to shade

Insects, Diseases, and Other Plant Problems: No significant problems. Invasive in many states including NC. See native alternatives to the left.

See this plant in the following landscape:
Cultivars / Varieties:
Tags:
#invasive#high maintenance#fast growing#aggressive#spreading#Noxious Weed List#federal noxious weed list#waterweed#aquatic weed
 
Cultivars / Varieties:
Tags:
#invasive#high maintenance#fast growing#aggressive#spreading#Noxious Weed List#federal noxious weed list#waterweed#aquatic weed
  • Attributes:
    Genus:
    Hydrilla
    Species:
    verticillata
    Family:
    Hydrocharitaceae
    Life Cycle:
    Perennial
    Country Or Region Of Origin:
    Asia
    Distribution:
    Nearly world-wide
  • Whole Plant Traits:
    Plant Type:
    Water Plant
    Weed
    Habit/Form:
    Spreading
    Growth Rate:
    Rapid
    Maintenance:
    High
  • 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:
    5a, 5b, 6a, 6b, 7a, 7b, 8a, 8b, 9a, 9b, 10a, 10b, 11a, 11b
  • Flowers:
    Flower Inflorescence:
    Solitary
    Flower Bloom Time:
    Fall
    Summer
    Flower Petals:
    6 petals/rays
    Flower Size:
    < 1 inch
    Flower Description:
    Small white flowers with 6 petals appear late summer to fall.
  • Leaves:
    Leaf Color:
    Green
    Leaf Type:
    Simple
    Leaf Arrangement:
    Whorled
    Leaf Shape:
    Lanceolate
    Leaf Margin:
    Serrate
    Hairs Present:
    No
    Leaf Length:
    < 1 inch
    Leaf Width:
    < 1 inch
    Leaf Description:
    Small, pointed leaves are arranged in whorls of 4 to 8. Margins are serrated and may have one or more sharp teeth under the midrib. About 1/2 inch long.
  • Stem:
    Stem Color:
    Green
    Stem Is Aromatic:
    No
    Stem Description:
    Long, branched green stems
  • Landscape:
    Problems:
    Invasive Species
    Weedy