FLOATING PENNYWORT

WATER PENNYWORT

Hydrocotyle ranunculoides

Pennywort Family [Hydrocotylaceae]  

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status
statusZneophyte
flower
flower8green
morph
morph8actino
petals
petalsZ5
stem
stem8round

7th Aug 2008, Reservoir, Compstall Navigation, Etherow Valley. Photo: © RWD
A very problematic and invasive alien plant of slow-moving or still shallow freshwaters such as ponds, lake-shores, canals and reservoirs. All the more unusual is that in its native land, America, it is declining rapidly almost to the extent of near extinction, which is a possibility.


7th Aug 2008, Reservoir, Compstall Navigation, Etherow Valley. Photo: © RWD
This is one of the first five invading, non-native aquatic plants to be banned from sale in the UK, which happened in 2014. Far too many householders with garden pools were finding that it smothered their ponds and fish and threw it out, into canals and other waters, where it quickly spread to become another problem there!


7th Aug 2008, Reservoir, Compstall Navigation, Etherow Valley. Photo: © RWD
Although it is called Floating Pennywort, here most are floating not on their leaves, but on their leaf-stalks. But the leaves do float as well, see further below. It looks like the long stems have many stringy white roots emerging at each node on the stem. The leaves grow to 70mm across.


7th Aug 2008, Reservoir, Compstall Navigation, Etherow Valley. Photo: © RWD


7th Aug 2008, Reservoir, Compstall Navigation, Etherow Valley. Photo: © RWD
This plant is another atypical Umbellifer. It flowers too, but so far your Author has not found any flowers. They are said to be small with pale-greenish-white to pale yellow in colour. The flowers themselves are between 2 and 4mm across, with 5 equal-length petals with a greenish midrib. The flowers are densely packed into a small hemispherical umbel about 15mm across of between 5 to 13 flowers. They have 5 white anthers splayed out from the base of the central green ovary. The fruits are small floating achenes which helps the spread of these unwanted weeds. The umbel of flowers appears above water on short a short stalk beneath the leaf.

Your Author thinks those paler-green small round things are growing leaves, rather than flowers.

The leaves have between 3 to 7 lobes with crenate teeth. They are round to kidney-shaped in overall outline.


Some similarities to : Navelwort and especially to Marsh Pennywort.

No relation to : Wall Pennywort [a plant with similar name]

This is a non-native invasive species that since 2003 has spread from just the River Chelmer in Essex to at least Manchester, and possibly far beyond. Unlike Marsh Pennywort Floating Pennywort has stalks at the edge of the larger leaves, and with the younger leaves resembling those of Water Crowfoot. Floating Pennywort likes wetter and deeper water than does Marsh Pennywort, and often has some leaves that are floating rather than standing like umbrellas above the water. There are currently enormous efforts in trying to eradicate this plant from Great Britain, or at least to try and stop it spreading further, but since it can re-generate from any short length of root left in the soil, and re-colonizes ponds in a matter of weeks from any one plant, this is looking like a forlorn hope. This plant was un-known in Britain before 1980. It has the potential to spread by 9 inches a day, and is choking up the River Soar so much that navigation by boat may soon be impossible, despite the enormous efforts to physically remove it (the environment agency bans chemical treatment to effect a solution).

For all its undesirability, it does possess one use; cows and horses love eating it, so it can be fed to them.

It reproduces by vegetative propagation from the smallest fragment left in the canal, and does so with some haste. It is problematic on many inland waterways of the UK now owned by the Canal & River Trust (CRT), and elimination of the weed is almost impossible because the smallest leaf left will quickly multiply, making its removal expensive and difficult.

The leaves vary in size from about an inch across to several inches, and either float or are held aloft on single stalks an inch or two above the waters' surface. The tiny flowers are fairly hard to find, are green or greenish-yellow, five-petalled and in umbels of 5 to 10, and was once thought to be an atypical Umbellifer, but is now re-allocated to the Ivy Family.

Despite its scientific name, Hydrocotyle ranunculoides, it is not to be confused with the Buttercup family of plants, or Ranunculaceae, and merely bears some resemblance to the Buttercups.

Floating Pennywort was previously ascribed to the Ivy family, but has since been moved into a family of its own, together with two other Pennyworts Marsh Pennywort and Hairy Pennywort; but not Wall Pennywort, which is a totally different plant.


  Hydrocotyle ranunculoides  ⇐ Global Aspect ⇒ Hydrocotylaceae  

Distribution
family8Pennywort  family8Hydrocotylaceae

 BSBI maps
genus8Hydrocotyle
Hydrocotyle
(Pennyworts)

FLOATING PENNYWORT

WATER PENNYWORT

Hydrocotyle ranunculoides

Pennywort Family [Hydrocotylaceae]  

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