Fallopia Japonica…

Fallopia japonica is an attractive plant that grows quite plentifully on the grass verges beside many of the local roads. The young shoots are edible, although very sour because they contain oxalic acid – the same acid that gives rhubarb its sharp taste. It is not related to rhubarb; neither is related to bamboo although it was first used in gardens to look like bamboo, but able to be planted in any type of soil or setting.

I first spotted an isolated patch between here and Coulonge a few years ago, then the patches became more noticeable and recently the council has taken steps to control them. When I arrived last July there were several large areas of roadside verge that had been dramatically cut back and sprayed.

The reason for this response is that Fallopia japonica is Japanese Knotweed and it is a non-native species in Northern Europe, and very hard to deal with. I have rarely seen it in England, although as a farmer’s son I was already familiar with the dangers of Giant Hogweed and Common Ragwort. Japanese knotweed is not poisonous but it is incredibly vigorous and almost impossible to kill. It completely takes over; out competing all the native species. When it is fully grown (at about 4 metres) its stems are like bamboo so it is physically very difficult to cut. It does respond to glyphosphate weedkiller which is absorbed by the plant and transported down to the roots, however the root system is very extensive and it only requires a small piece to survive for the plant to start growing again. Japanese Knotweed produces very deep root structures called rhizomes that store food and from which new plants can grow. They can be dug out but they go remarkably deep and it is hard to be sure that you have found every bit. This is why the plants spread so effectively and, even if you kill off the visible signs, new growth is sure to follow. Indeed, there is new growth visible over most of the treated patches here in France.

Reproduction through rhizomes is an example of vegetative propagation, a form of asexual reproduction (I wrote a little about asexual reproduction in this post on fungi). Fallopia japonica will not produce seeds in the UK because the conditions are not right, which means that every plant you encounter will be a genetic clone of the original plant introduced to Holland by explorer Philipp von Siebold in the 19th Century. It travelled to Britain as an exhibit at the Botanic Gardens at Kew in 1850 and has been loving life in the UK ever since.

The trick to its removal seems to be repeated spraying or digging so that the rhizomes are slowly depleted of their food reserves. It will take several seasons to completely eradicate an established patch. In the UK they have finally decided to choose a biological control method. An insect called a psyllid that eats Japanese Knotweed is being introduced to the country. There are many different types of psyllid but, thanks to co-evolution, they are very specific feeders on their target plant. This reduces the risk that they will attack some other native crop. It should also mean that the control is self limiting – when the knotweed is destroyed the psyllid will disappear too.

The video below is from a few years ago but it does describe the problem of Japanese Knotweed well and what has been done to deal with it over the last decade or so.

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Questions…

1. What do you expect the pH of oxalic acid is likely to be?
2. Suggest something for which a Japanese Knotweed and a native species might compete.
3. Which vessels within the Japanese Knotweed will carry the weedkiller down to the roots?
4. Suggest a function of plant roots not mentioned in the passage above.
5. Apart from vegetative propagation, describe another method of asexual reproduction.
6. What is a clone?