Invasive Aliens After an incredible sequence of misadventures he was finally reunited with what remained of his collections in Leiden, The Netherlands, in 1842. There he set about forming his Royal Society for Opening Pandora’s Encouragement of Horticulture. Preserved in its journal the Jaarboek van de Koninklijke Nederlandsche Maatschappij tot Aanmoediging van den Tuinbouw , are a complete series of seed packet dated and priced catalogues of Von Siebold & Co. Anyone who has ever worked on the history of plant introductions will appreciate what a stroke of fortune this was, since Japanese knotweed arrived as a sought-after exotic plant plant catalogues of this date are extremely but is now a proscribed alien. John Bailey explores some difficult to come by. In the 1848 edition of the Siebold & Co of the unpredictable outcomes that have arisen for these catalogue, the category ‘ newly indestructible plants. imported from Japan’ includes a range of species with prices from 300-600 francs. sieboldii (Japanese knotweed) was available only as a collection of one mother plant and 25 strong plants for the apanese knotweed ( japonica) had sum of 500 francs. There is a seven-line been minding its own business in Japan footnote extolling the virtues of this and China for millennia. On volcanoes in J wonderful plant, which can do practically Japan the dwarf form of the plant (F. japonica anything, short of bringing back the dead! var. compacta) had the habitat to itself, and Given that 500 francs spent in the same was the primary coloniser of volcanic ash catalogue would have filled the barouche fields. Long association with sulphurous landau to overflowing with choice emissions and sudden depositions of hot ash ornamentals - this was an extremely endowed it with certain tenacity. The high expensive plant. altitudes meant a much restricted growing Siebold was, of course, nobody’s fool. In season, early flowering and dwarf habit. Key order to make money on a plant as readily to its survival was the woody that propagated as this, you needed a high initial went vertically downwards, where stored price. Indeed by 1856 24 plants could be had nutrients and dormant buds were beyond for only 6 francs! the reach of the next deposit of hot ash. In The next step in 1850, was to send a such habitats, plants are characteristically package of plants, including Japanese separate clumps not connected by knotweed to Kew Gardens in the hope of underground . extracting further novelties in exchange. The tall lowland forms of the plant (F. John Bailey is Principal Experimental This is all duly recorded in copperplate Officer in the Department of Biology at the japonica var. japonica) faced a different set of handwriting in the Kew Inwards Book, along University of Leicester, where he has been problems. In Japan they were just one with a terse note saying that on account of working since 1977. A colleague in the component of a giant herb community, bad selection only six of them were new to department, Ann Conolly, introduced him either competing with such plants as the gardens. to Japanese knotweed, and after her Miscanthus and bamboo, or trying to find a Contemporary illustrations show that the retirement he carried on from where she space in a forest clearing or riverside. Here Siebold plant is actually male-sterile, with left off. After completing a PhD on it, he the rhizome may have acquired the maintained a strong interest in the plant secondary function of seeking out new and established many international resources of space, light and evasion of collaborations. The adoption of molecular predation. approaches in the 1990s and the hard work of two PhD students greatly extended the scope and impact of the research, resulting Siebold’s plants in his contribution to more than 30 In order to find out how Japanese knotweed scientific papers on the subject. It is his came to end up in Britain and cause such proud boast that he is more interested in problems, one must delve into the currently the sex lives of these plants than he is in rather unfashionable area of the history of eradicating them. Invitations to lecture on botany. Philipp von Siebold was a most the subject have taken him as far afield as Japan and the US. He now has his sights colourful character, whose name is attached set on New Zealand and is currently as the authority to many of the Asiatic looking for funding to take this research species that we now take for granted in our gardens. As a surgeon he was able to travel

further. P h o

to Japan with the Dutch trading delegation at t o :

R o

a time when Japan was effectively closed off y a l

B

from the rest of the world. In spite of being o t a n i c

restricted to an artificial island in the G a r d

harbour at Nagasaki, his knowledge of e n s

K

advanced western surgical procedures won e w him many friends in Japan, who in return Manuscript RBG Kew Inwards book 1848-1858 provided him with choice Japanese plants showing the list of plants sent by Siebold in 1850. that gardeners in the West were keen to Item 34 ‘Polygonum Sieboldii’ is more commonly known as Japanese Knotweed (Fallopia japonica possess. var. japonica) .

THE HORTICULTURIST APRIL 2010 21 the 1960s and 1970s, and displayed in a series of dated distribution maps. Some of the earliest non-garden records came from Welsh coal-mining valleys and it is possible that, rather than escapes, these were examples of deliberate planting, since one of many claimed benefits of the plant, was stabilisation of loose soil; coal barons no doubt keen to try anything that allowed their e c

spoil heaps to be more vertiginous. n e i c s o i B

I B A C

Cause for concern : o t o h

By the late 1970s the true extent of the P spread of Japanese knotweed in the UK was A nymph of Aphalara itadori, the approved bio-control agent for Japanese knotweed . becoming apparent, and clearly some influential people were beginning to get rattled. Accordingly, when the wide-reaching Eradicate… Wildlife and Countryside Act was published P

h Overnight the industry of Japanese knotweed o t

o in 1981, provision was made for the :

R eradication was born, and suddenly o

y proscription of alien plants and animals that a l

B developers took a serious interest in botany, o

t it was felt were particularly harmful to the a n

i with knotweed-infested sites selling at c

G environment, Japanese knotweed being one a

r serious discounts. Guaranteed eradication d

e of two land plants so listed. I will not dwell n

s was an expensive business, with developers

K

e on the almost 30 years it has taken for any w fearful equally of prosecution and the of the many other deserving contenders to Contemporary illustration of Siebold’s Polygonum possibility of any of the ‘armour-piercing’ be added to this list, but examine the strange sieboldii (Japanese knotweed). rhizome being left on their sites. Major consequences of Japanese knotweed being sporting venues such as Wembley and many on it in the first place. of the London Olympic venues have been hit cordate leaf bases. The fact that only the The offence to ‘plant or otherwise cause by these costs. Costs, incidentally, that are female form of a dioecious species was the plant to grow in the wild’ was long incurred only in the UK - other European originally imported has had a number of deemed to exclude movement of viable countries apparently being able to survive important consequences. Firstly, it could not rhizome fragments by road works and without such legislation, which is, I reproduce itself by seed. Not a major issue, redevelopment schemes and was perhaps maintain, an entirely unintended when as little as 0.8gm of rhizome could more suited to evil-doers planting it in consequence of including Japanese give rise to a new plant. Secondly any seed nature reserves at the dead of night! This all knotweed in the 1981 Act. collected from it would inevitably be hybrid, changed with the Environmental Protection In the UK press Japanese knotweed so later on when male plants of the related Act of 1990, when the pendulum swung regularly attracts epithets, such as ‘monster’, giant knotweed (F. sachalinensis) became abruptly to the other extreme. It became an ‘barbarian’ and ‘triffid’, but in spite of the available, seed could be collected from offence to move as much as an atom of mythology surrounding it, if caught early Japanese knotweed from one site to another enough, it is readily eliminated by the use of unless it was in specially sealed and “It became an offence a range of herbicides. Problems arise in the decontaminated lorries delivering it to treatment of long established stands, where to move as much as an officially designated deep landfill sites. atom of Japanese decade after decade, the network of woody knotweed from one site to another unless it was in specially sealed and decontaminated lorries delivering it to officially designated deep landfill sites. ”

Japanese knotweed and distributed as Japanese knotweed seed. This seed was of course the hybrid now known as Fallopia x bohemica (after its original description in the Czech Republic), and is a widespread, if under-recorded, component of Japanese knotweed populations throughout the West. We now enter the ‘Dark Age’ of Japanese knotweed knowledge where the only evidence of its existence comes from dated n a v herbarium specimens, and the occasional e B

d i v published note of where it had become a D

: o t

abundant. The early history of its o h introduction was carefully pieced together by P the painstaking research of Ann Conolly in F. x conollyana at its type locality in Haringey North London, with Ann Conolly in attendance.

22 THE HORTICULTURIST APRIL 2010 all the Japanese knotweed (Fallopia japonica var. japonica) was a single clone, and that useful variation in the chloroplast DNA existed in plants sent directly from China and Japan. Catherine Pashley then came on the scene with the intention of comparing the chloroplast patterns found in the European clone with those of plants collected from a wide survey of Japan, thereby establishing the origin of the imported plant. It is one of the basic tenets of biological control that you should understand the and reproductive biology of the organism to be controlled, and also know where the particular genotype evolved. That Japanese knotweed was already known to be a clone, was a bonus, since once a suitable control organism was found, the plant would not have any reserves of resistance to it. It is necessary to know the area of origin, so that the appropriate control agents can be sought in this area. Historical and morphological data had already ruled out China as an origin of our clone, but although Japan is not a large country, it is extremely long, with varied habitats and dissected by mountains. After much hard work, a matching genotype was found in Nagasaki, which perhaps unsurprisingly was near where Siebold was based during his Japanese sojourn. After a considerable amount of testing, CABI announced in 2009 that a suitably specific control agent had been identified, a pysllid sapsucker Aphalara itadori , which in greenhouse trials had devastated the knotweed plants. Whilst continuing to work on some promising micro-organisms, CABI applied for permission to release the psyllid last year. Permission was granted in early 2010. The release, due in spring/summer 2010, will be y e l i a on a phased basis, at two or three closely- B n h o

J monitored sites. As with all bio-control

: o t o

h programmes, the aim is to weaken rather P Eroded surface on Mount Aso, Japan, showing the than eradicate the target organism, and deep and extensive woody rhizomes of the montane existing control measures and public F. japonica. ignorance to a textile manufacturer as to the necessity of incorporating expensive copper education will remain an essential part of filaments in such membranes! the campaign against Japanese knotweed. underground rhizomes has increased in girth Japanese knotweed’s struggle to survive in and range, effectively producing an its native habitat is in stark contrast to the Unpredictable outcomes ‘underground tree’. profligate vigour it exhibits in the West. This We are all familiar with the potential Above ground growth and re-growth will is down to a more than suitable climate, dangers to the environment posed by alien be decimated by the appropriate systemic absence of competition in ruderal areas and invasive species, which freed from the herbicides, but die-back does not extend far a more or less complete absence of attention constraints of the area in which they enough into the rhizome to eliminate it. One from native invertebrates. In Japan it is host evolved, are often capable of out-competing can soon reach a stalemate with such to a range of invertebrate predators, with the the local species and having a major stands, whereby only small mal-formed different groups targeting different plant negative impacts on biodiversity. There is shoots show, presenting little surface area organs. The other obvious method of control however, a less well-known danger for absorption of further systemic treatment, is to reintroduce the plant to some of the associated with plant introductions - the yet the plant is not dead. Improvements in enemies that have been left behind in the creation of new species by allopolyploidy. the timing and method of application of area of origin - biological control. This can occur when two distantly related herbicide, such as stem injection in the plants hybridise to produce a sterile F1 - autumn, are helpful but other approaches sterility arising from the failure of the are also necessary. Biological control chromosomes of the two genomes to pair at On redevelopment sites, which do not have CABI Bioscience and its predecessors have a meiosis. If followed by chromosome the luxury of several seasons of treatment, distinguished history in this area, and in the doubling, at a stroke fertility is restored and other solutions, such as on-site burial sealed late 1990s, whilst planning a collecting trip a new allopolyploid species is created. under geo-textile membranes, are to Japan we were approached by Dick Shaw The most important case of allopolyploid preferable. But even here we are verging on of CABI. Work at Leicester by Michelle speciation was in the evolution of the the metaphysical. I readily admitted my Hollingsworth had already established that hexaploid bread wheat - without which - I

THE HORTICULTURIST APRIL 2010 23 her F. japonica var. spectabile Japanese knotweed. Indeed the thought of combining the vigour of the two parents and adding a pinch of heterosis (hybrid vigour) does rather conjure up a triffid like scenario! Fortuitously, the opposing over-wintering strategies tend to cancel each other out, and whilst F. x conollyana is a perfectly viable plant, and can with time, establish large stands, it is not a particularly aggressive plant. New Zealand

y Just when I thought (not for the first time), e l i a B that my work on Japanese knotweed had run n h o J

: its course, I received seed collected from o t o h

P some New Zealand Japanese knotweed Typical monoclonal stand of Fallopia japonica var. japonica along the River Wnion at Dolgellau, Wales. plants. It germinated well and once again I Russian was presented with some twining plants Hybridisation between Japanese and giant with 54 chromosomes. Russian vine, would not be sitting here writing this article! knotweed, is of course nothing remarkable, however, was not known from that area, In historical times we have witnessed two since both species are closely related and and it appeared that we actually had hybrids cases of amphiploid speciation in the wild in both occur in Japan. Far more extraordinary between an indigenous Muehlenbeckia and Britain, Spartina anglica and Senecio is the hybrid between Japanese knotweed Japanese knotweed! cambrensis . The key similarity is that both and Russian vine. Collect seed from any From an academic viewpoint this is involved hybridisation between a native Japanese knotweed plant in an urban area remarkable in terms of the length of time British species and an introduced species, and the chances are that it will have been that has elapsed since these two plants had the outcomes of the speciation events are pollinated by Russian vine. The presence in last shared a common ancestor. In practical rather different. Spartina anglica was so the West of large areas of female japanese terms, this is a much more compatible successful at reclaiming mudflats, that in knotweed actually constitutes a huge hybridisation than the one producing F. x addition to out-competing its British parent, inadvertent breeding experiment, and conollyana , since both parents bring it has been widely distributed round the anything that can possibly pollinate it will complementary features to the hybrid. world for this purpose, and considered an have done so. Apart from their extreme Considering that on alien invasive in many regions. Senecio vigour and garden origins, these two plants its own is able to produce impenetrable cambrensis on the other hand, was produced would appear to have little in common. thickets, Pandora’s seed packet may yet at a period when wartime bomb damage, Russian vine is a diploid woody climber have some triffid-like surprises waiting for followed by the wide-scale redevelopment of q with 20 chromosomes and Japanese us! the 1960s and 1970s, created the habitat that knotweed is a rhizomatous herb with 88 it favoured. But its numbers are now chromosomes, and they originate from declining with the reduction of derelict land. Useful links different parts of Asia. They are of course The key requirement for allopolyploidy is Cornwall Knotweed Forum distantly related, and members of the the bringing together and hybridisation (http://projects.exeter.ac.uk/knotweed) , and if the differences in between, distantly related plant species that growth habit are ignored they have a lot of Knotweed biological control have long been kept apart by various floral and morphological characters in (www.cabi.org/japaneseknotweedalliance) geological events. The seemingly relentless common. Some years back, I well recall the Child L, Wade M. (2000). The Japanese quest for horticultural novelties is constantly horror of Beth Chatto, when I offered her Knotweed Manual . Packard Publishing bringing such species together. Whilst the some of this hybrid (now known as F. x Chichester (ISBN 1853411272). chances of this happening are not very high, conollyana 2n=54), in exchange for some of and the outcomes not always necessarily bad, the pre-requisite for this is the presence of sterile F1s between distantly related species. Work at the University of Leicester over the years has revealed some extraordinary features of the Japanese knotweed sensu lato (s. l.) population structure. Firstly, in spite of its clonal nature it has successfully spread to 2,761 of the 3,859 10km recording squares in the British Isles. As a female plant it can only produce seed by hybridisation - in this it has been extremely successful. F. x bohemica , the hybrid with giant knotweed occurs at four different chromosome ploidy levels (44,66,88 & 110), and is capable of backcrossing to its female parent. This is why I use the term Japanese knotweed s.l. to cover F. japonica, F. sachalinensis, F. x bohemica and any back-crosses. So in spite of its initial clonal nature, extensive hybridisation has not only created new variation, but also produced more vigorous Japanese knotweed is not always a blot on the landscape, here in North Ledaig (Scotland), F. japonica var. individuals that are more difficult to control. compacta makes an attractive scene.

24 THE HORTICULTURIST APRIL 2010