Research at Leicester

My main work is on the history, origins, occurrence, spread and hybridisation of Japanese Knotweed (Fallopia japonica), Giant Knotweed (Fallopia sachalinensis), Fallopia x bohemica, F x conollyana  and any backcrosses between the parent plants and their hybrids. Although this research is centred in Europe I am also interested in what is going on in other countries such as the USA where this plant is also regarded as a nuisance.  I have been publishing papers on the subject since 1985. This research has been through a number of phases, starting with distribution and morphology it moved on to cytology and hybridiisation, and is now enjoying the imput of molecular technique which allow us to ask and answer many more questions.

In this research I have been very ably assisted by two PhD and one MSc students.

At Leicester we maintain a living collection of nearly 1000 accessions from all around the world, including a range of wild and artificial hybrids.  These are all backed up with voucher specimens deposited in our herbarium LTR.

As with all good aliens we are asking three questions about Japanese Knotweed and its relatives: Where do you come from, and why and what are you doing here?

Where do they come from?

In nature Japanese Knotweed is found in Japan, Korea and China. Giant Knotweed is found in Northern Japan, Korea and Sakhalin Island.  In order that potential Biological Control agents may be identified, it is vital to know which part of which country these different plants originated from.  Both historical and morphological data indicate Japan as the most likely candidate for F. japonica, whereas Japan and Sakhalin are equally likely sources of F. sachalinensis.  Using data from chloroplast DNA sequences it is possible to establish regional markers for individual clones of these plants.  Work by C. Pashley on the chloroplast markers of a large collection of live plants collected throughout Japan is now almost complete.  This should give us a clearer idea of where the British clone of F. japonica originated.  Similar data comparing British and Japanese accessions of F. japonica var. compacta and F. sachalinensis is also nearly complete, though we still lack material of known Sakhalin provenance.

The hybrid between F. japonica and F. sachalinensis  (F.x bohemica) most probably occurred after the plants had been introduced to Europe.  Since when gardeners grew the two species together, any seed collected from the F. japonica parent would be hybrid with the F. sachalinensis.  Further, the hybrid has only been recorded very recently from Japan itself.  Further details in: Bailey et al. (1996).

Why are they here?

This question is quite easy to answer from historical records and literature - they were deliberately introduced, primarily as garden plants, where their statuesque growth-form and reliable white autumn foliage were originally much admired.  Their prodigious productivity did not go unnoticed, and F. sachalinensis in particular was promoted as fodder for cattle.  Japanese Knotweed was initially offered for sale with a hype verging on the criminally optimistic!  No part of this wonderful plant seems to be without some valuable use. In addition to being a beautiful garden plant, the gracious inflorescences could be used as cut flowers and supply autumn nectar to the bees, the foliage was, it seems, irresistible to cattle, the strong roots contained both a tonic principle and stabilised sand dunes and spoil heaps - even the attractive dead stems (should you be able to bear to part with them) could be used to make matches!  Bailey & Conolly (2000).

What are they doing here?

Well that is the 64,000 dollar question! There is a parallel with what was once said of American GIs in Britain during the war; 'over-fed, over-sexed and over here!'  These plants are certainly giants, they hybridise promiscuously and in spite of all our efforts to eliminate them, they are certainly over here to stay!

Molecular research by Hollingsworth indicated that all the Japanese Knotweed in Britain belonged to a single female clone, and that the same clone was also present in continental Europe and the USA.  This means that they are just parts of one gigantic organism, and its total biomass may make it the largest female in the world.

More seriously, rounds of hybridisation and back-crossing can in theory lead to the production of new fertile species, better suited perhaps to their new habitat in Europe.  The hybrid F. x conollyana (Japanese Knotweed x Russian Vine) has been popping up all over Europe, but has yet to be reported from the USA, is currently a sterile pentaploid 2n=54, but is only a chromosome doubling away from becoming a new fertile species. F. x bohemica is probably going to be found to be more invasive than either of its parents, and is known to regularly back-cross with both of its parents at various British localities. Bailey, J.P. (2001)

The other main research theme at Leicester is into the dynamics of the origin and spread of the three different ploidy levels of Fallopia x bohemica hybrids in Britain.  This is being done through the use of ISSR molecular markers, which can identify how much genetic variation is found at any particular site. It can also match like-individuals at widely separated sites and so hopefully show patterns of spread.

Pashley, C.H., Bailey, J.P. & Ferris, C. (Submitted)

How can I help?

We are very keen to obtain live rhizome samples from China, Japan, Taiwan, Korea and North America to assist with our cytological and molecular genetical studies. We are very interested in receiving the locations of F. x bohemica plants from Britain and around the world. We would like to know the sex of plants found outside the native range of Japanese knotweed (i.e. excluding Japan, China and Korea).  We would also like to know if these plants have been introduced to South or Central America, India, Africa and Cuba, and to gain a more accurate record of the range of this plant in North America. 

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Research at Leicester Control  Biological Control  History 
F japonica Life cycle F x bohemica F sachalinensis F x conollyana
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