Characteristics to Identify Some of Washington's Noxious Aquatic Weeds and Native Look Alikes


Myriophyllum aquaticum (parrotfeather) - Non-native plant and state-listed noxious weed 

·      Emergent leaf stalks - very distinctive and not easily confused with other species

·      Bright green foliage looks like tiny fir trees on the waters surface

·      Usually 5-8 leaves per whorl (arranged around the stem) 

Myriophyllum spicatum (Eurasian watermilfoil) - Non-native plant and state-listed noxious weed

 ·      Mature leaves with 14-24 leaflet pairs, at about a 45 degree angle to the length of the leaf

·      No winter buds produced

·      Floral bracts smaller than the flowers

The following two native species are very similar in appearance to Eurasian watermilfoil: 

Myriophyllum sibericum (northern milfoil) - Native plant look alike 

·      Mature leaves with 4-14 leaflet pairs from a 45-degree angle to almost perpendicular to the leaf length

·      Cylindrical winter buds

·      Flower bracts smaller than the flower 

Myriophyllum verticillatum (western milfoil) - Native plant look alike

 ·      Mature leaves with 9-17 leaflet pairs

·      Pinnate floral bracts, larger than the flower

·      Club-shaped winter buds

NOTE: DNA testing confirmed milfoil hybrids present in Washington. Sometimes plant specialists need to rely on DNA testing to confirm milfoil species. When in doubt, ask an expert.


 Egeria densa (Brazilian elodea) - Non-native plant

 ·      Typically 4 leaves per whorl, to 4 cm long

·      Minute serrations along the leaf edges, but you need magnification to see the serrations

·      Male flowers only, up to 2 cm across

·      No tubers

Hydrilla verticillata (hydrilla) - Non-native plant

 ·      5 leaves per whorl - less leaves per whorl early in the season, 1-2 cm long

·      Visibly toothed leaf edges

·      Tiny white flowers

·      Tubers present (very diagnostic for hydrilla because similar-looking species do not have tubers)

Similar Appearing Native Species: 

Elodea spp. (American waterweed) - Native plant look alike

 ·      3 leaves per whorl, usually less than 2 cm long

·      Need magnification to see the serrated leaf edges

·      Tiny white flowers

·      No tubers

·      Very common in Washington lakes


Cabomba carolineana (fanwort) - Non-native plant and state-listed noxious weed 

·      Opposite fan-shaped leaves on long stalks

·      Small floating leaves are present when growing to the water surface 

Similar Appearing Native Species: 

Ranunculus aquatilis (water buttercup) - Native plant look alike

 ·      Fan-shaped alternate leaves

 Megalodonta beckii (marsh marigold) - Native plant look alike

 ·      Fan-shaped opposite leaves, but the leaf stalks are so short that the leaves appear whorled.


 Utricularia inflata (swollen bladderwort) - Non-native plant

 ·      Radiating wheel-like float supports the flower stalk

·      Small-coiled winter buds

·      Yellow flowers

Similar Appearing Native species: 

Utricularia vulgaris (common bladderwort) - Native plant look alike

 ·      No float on the flower stalk

·      Large ball-shaped winter buds

·      When neither structure is present, these two species are extremely difficult to distinguish

·      Note there are several rare bladderwort species present in Washington 


Lythrum salicaria (purple loosestrife) - Non-native plant and state-listed noxious weed

 ·      Pink/purple flowers with 6 sepals, 6 petals,12 stamens

·      Fruit -a 2 valved capsule

·      Generally opposite leaves

·      Square stem

·      Reproduces by seeds and adventitious buds on buried stems (growth stimulated by disturbance)

Lysimachia vulgaris (garden loosestrife) - Non-native plant

 ·      Leaves opposite or whorled

·      Leaves soft-hairy, dotted with black or orange glands

·      Flowers showy and yellow, 5 petals, fruit is a dry capsule


Epilobium hirsutum (hairy willow-herb) - Non-native plant

 ·      Showy pink-red flowers with 4 sepals, 4 notched petals, 8 stamens

·      Round stem

·      Long seed capsules that split open and release the fuzzy coated seeds

·      Leaves are opposite and hairy, toothed


Phalaris arundinacia (reed canarygrass) - Likely exotic ecotype and state-listed noxious weed

 ·      To 6 feet tall, stem 0.5 inches wide

·      Leaves 0.25 to 0.75 inches wide

Phragmites austalis (common reed) – Non-native genotype – state-listed noxious weed

 ·      To 12 feet tall

·      Sheath of the leaf blade is smooth and loose allowing leaves to twist in the wind

·      Flower spikes feathery

·      Common reed may be confused with native populations of Phragmites. Native genotypes are less dense; the stems are thin and shiny. The flowers are also less dense.


Nymphoides peltata (yellow floating heart) - Non-native plant and state-listed noxious weed 

·      4-6 inches across water lily-like floating leaves with a slit

·      Yellow flowers with 5 fringed petals, held above the water's surface

Ludwigia hexapetala (water primrose) – Non-native plant and state-listed noxious weed

 ·      Yellow flowers with 5 sepals and 5 petals

·      Alternate leaves

·      Erect stems

Ludwigia peploides (floating primrose willow) – Non-native plant and state-listed noxious weed 

·      Looks very similar to Ludwigia hexapetala – consult a plant expert for identification.

·      There are no native look-alikes for either species