Elodea nuttallii

Frogbit Family [Hydrocharitaceae]

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Photo: © Sue Heath
An aquatic freshwater weed growing to 3m in shallowish ponds, lakes, canals or slow-flowing rivers and streams. Like Curly Waterweed (Lagarosiphon major) it is highly branched.

Photo: © Sue Heath
Unlike Curly Waterweed not all leaves are strongly recurved.

Photo: © Sue Heath
And perhaps unlike Curly Waterweed the leaf-nodes are reddened.

Photo: © Sue Heath
Flowers are infrequent, and interspersed at random intervals along the long stems. They are on long stalks within a sessile axillary spathe (as are those of Curly Waterweed). The flower (top right, but not yet open here) floats on the surface.

Photo: © Sue Heath
The flowers are tiny, 2 or 3mm across, with 3 petals. They are dioecious having male and female flowers on separate plants, with only female plants occurring in the UK. Unlike Curly Waterweed which has reddish flowers in pairs with 3 sepals and 3 petals and either 3 stamens or 3 styles, Nuttall's Waterweed has whitish to reddish flowers with 3 sepals, 3 petals and either 9 stamens or 3 styles. Unfortunately, both plants have reddish or whitish flowers in pairs with 3 sepals, 3 petals, petals as large as sepals, with the flower arising inside an axillary spathe. The only two differences your Author can see between the flowers of the two plants is that on Curly Waterweed) there are several flowers (rather than just one) if the plant is male and 9 stamens on male plants (rather than 3 of Nuttall's Waterweed) [unfortunately, in the UK, both plants are all female!]. So, all taken together the Author concludes that there is no reported difference in the UK between the flowers of Nuttall's Waterweed and Curly Waterweed, even though both belong (at present) in differing Genera.

Photo: © Sue Heath
Your Author is not sure whether these 'teeth' are just the ends of leaves, or on the stem.

Photo: © Sue Heath
The teeth are minute, as are those of Curly Waterweed

Photo: © Sue Heath
Two similar aquatic weeds: Curly Waterweed top left; Nuttall's Waterweed (Elodea nuttallii) bottom. Both similar, both branched, but the latter has leaves always in whorls (never spirals), the whorls being of usually 3 to 4 (2 to 5 being the extremes).

Photo: © Sue Heath
Curly Waterweed top left; Nuttall's Waterweed bottom. The latter is also a much paler green/lime green and with reddened portions where leaves meet stem. The leaves on Nuttall's Waterweed are not all strongly recurved, some being straightish or wavy and are always minutely serrate (rather than wavy or minutely serrate on Curly Waterweed).

Easily confused with : Curly Waterweed (Lagarosiphon major) - slight differences depicted in the photo captions.

Not to be semantically confused with : Pondweeds (Potomogeton species) or Duckweeds Lemna species [aquatic plants with similar names]

Easily mis-identified as : Canadian Waterweed (Elodea canadensis) and South American Waterweed (Elodea callitrichoides) which both belong to the same genus as Nuttall's Waterweed, Elodea. Any differences are mostly confined to either minute or small dimensional differences requiring either a micrometer or a measuring loupe; or to the number of leaves in a whorl, as averaged over the whole plant (or plants). Canadian Waterweed has whorls of 3 ± 1; Nuttall's 3-4 ± 1, but South American has whorls of 3 (only?). All three are non-native to the UK and are found in shallow freshwater as throw-outs from garden ponds, or are spreading vegetatively from previous throw-outs.

Like Curly Waterweed (Lagarosiphon major) (which belongs to the Lagarosiphon genus) Nuttall's Waterweed is dioecious, with separate plants bearing male and female flowers. And like that, only the female plants are found in the UK. They are non-native and escape vegetatively into waterways when folk carelessly throw excess weeds out of their fish-ponds into other waters where they can then become a nuisance.

  Elodea nuttallii  ⇐ Global Aspect ⇒ Hydrocharitaceae  

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Elodea nuttallii

Frogbit Family [Hydrocharitaceae]