Aquatic Plants

Hydrocotyle ranunculoides or Floating Pennywort

In late April 2003 I picked up a piece of water plant from the lode in Soham and 'installed' it in our newly created garden pond. The plant flourished.

The first photo below is of a pair of damsel flies in process of depositing their eggs, perched on a leaf of the plant in our pond. Also with the plant are floating leaves of water starwort. This photo was taken about 3 weeks after installing a 30cm length, which shows its rapid growth!

By August, the plant had spread itself around two sides of our pond which measures about 3 by 3.5 metres. It had also embedded some of its runners in the turf around the pond edges.

However I had still not identified it as it was not included in any of the several wild plant books I possess. So I emailed the Natural History Museum, describing the plant. Yes, I could send them a specimen. However, if it was what I though it was, the expert to contact was a Dr .... (I shall not give a name here). He lived in Warboys - which is not a huge distance from myself. So I phoned the good doctor and described the plant.

That sounds like Hydrocotyle Ranunculoides he told me. It's a recognised biological hazard of a plant and if you find it in UK waterways, you should inform the appropriate authority. We discussed other identifying features and, knowing a name to search for, I did a Google search for Hydrocotyle Ranunculoides. There are a lot of mentions!

I had in fact thought that the leaves did indeed resemble those of Hydrocotyle vulgaris - the marsh pennywort, which is a common UK water plant and which I also had in the pond. I had not realised that it, too, might be a hydrocotyle. I had thought it looked most like an unusual batrachian ranunculus - maybe not such a bad guess as is is hydrocotyle ranunculoides

It has several features:


Turns out it's a 'Bill Gates' of the water plant world!

Having identified it, it suddenly became a good deal less attractive and we immediately removed armsfull of the stuff from the pond. Not too difficult as the pond has a butyl liner, However, where it's established itself in the turf, removal is not a quick process. However I don't think it will survive in the lawn for long, as it should not take much mowing!

The plant dies back in winter, but shoots and roots survive in the bank and mud and these quickly grow into new plants in spring. The plant is nearly as happy growing free in the water as it is growing on mud: when floating in the water the roots and stems (photo 4) form a tangled, floating mat from which the leaves emerge. The plant has phenomenal growth abilities and can quickly choke a river.

As a flowering plant, it scores zero points: the flowers, though compound, are tiny and insignificant, so it's quite difficult to find them. The second photo shows a flower - as you can see it's compound, and the Hydrocoytlye family is related to the umbellifers.

On August 31st 2003, we took a look at Soham lode to see what was the situation. It is indeed well established in Soham Lode: the mill pond at map reference TL 589 730 is dominated by large drifts of it and there are plenty of vigorous growths of HR down stream as far as I investigated, to the railway line at map reference TL 585 730.

The first picture in the second row show a mats of the plant in Soham lode and the second is view of the Mill pool where it is now a dominant species.

The plant is a fine and beautiful pond plant - if you have a liner so that it cannot get well established in the margins. However it is dangerous and if you should have it in your pond, be very careful not to introduce it into any natural waterway or pond.

Should you find it in the wild, contact your nearest Environment Agency branch and inform them. It is a very fragile plant that grows easily from a single node. The leaf nodes are about 30mm apart so it only takes a tiny fragment to spread the plant.

Afterword

I first reported the plant in Soham lode in 2003 when the environment agency attempted to eradicate it. However in 2007 it was recorded in the main River Cam and by 2010 it had become a serious nuisance and very abundant. The last photo shows the River Cam or Granta in 2016 above Cambridge, blocked by rafts of Hydrocotyle Ranunculoides.

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Last modified: Wed, 10 Jan 2018 11:03:19 GMT
Page first published 13th September 2003
Page written and © 2003 - 2018 Richard Torrens