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JAPANESE, GIANT AND
BOHEMIAN KNOTWEED
(Fallopia japonica (H.) R D.,
F. sachalinensis (F. S) R D.
and F. ×bohemica (C et C) J. P. B)
L B
Department of Natural History, Savaria Museum,
Pf. 14, Szombathely, H-9701, Hungary;
bala_lajka@hotmail.com
Tax onomy
A) Scientific name: Fallopia japonica (H) L.P. R D in R D A-
1988; synonyms: Reynoutria japonica H 1777; Polygonum cuspidatum S et Z-
1844; P. sieboldii D V 1849, non M. in DC. 1856; P. sieboldii hort. ex M
(sensu C & F 1994); P. giganteum hort.; P. confertum H fil.; P. r e y n o u tr i a M-
1901; P. zuccarinii S 1895; Pleuropterus zuccarinii (S) S 1933; Pl. cuspidatus (S.
et Z.) H. G 1913; Tiniaria japonica (H.) H 1946; Common names: UK: Japanese
knotweed, Sally rhubarb, donkey rhubarb, gypsy rhubarb, Hancock’s curse, broad-leaved polygonum;
USA: Mexican bamboo, Japanese bamboo, Japanese fleece-flower, wild rhubarb, crimson beauty, ele-
phant-ear bamboo.
B) Scientific name: Fallopia sachalinensis (F. S P.) L.P. R D in R
D A 1988; synonyms: Reynoutria sachalinensis (F. S P.) N in
T. M 1922; Polygonum sachalinense F. S P. e x M 1859; Pleuropterus sa-
chalinensis (F. S P.) H. G 1913; Tiniaria sachalinensis (F. S P.)
J 1950; Reynoutria sachalinensis va r. brachyphylla H; R. brachyphylla (H) N 1938;
R. ×vivax S & S 1985 (sensu C & F 1994, et K 1999); Common
names: UK: giant knotweed; USA: Sakhalian knotweed, elephant-ear bamboo, Sacaline, Sakhaline.
C) Scientific name: Fallopia ×bohemica (C C) J.P. B 1989; synonyms: Reynou-
tria ×bohemica J. C A. C 1983; R. ×vivax J. S K.J. S 1985; R. ×vivax
auct., non S S 1985 (sensu C & F 1994); Polygonum ×bohemicum (J.
C A. C) P.F. Z A.L. J ; (= F. japonica × F. sachalinensis); Common
names: Bohemian knotweed; hybrid knotweed.
e family of knotweeds (Polygonaceae) belonging to the order of Polygonales comprises about 40 gen-
era. e taxonomy and nomenclature of species dealt with in the present study have changed many times.
Taxa that were earlier classified into the genera Reynoutria, Polygonum, Tiniaria, Pleuropterus and partly
also Bilderdykia – are recently specified, based on chromo some analyses, as belonging to the genus Fallopia
e most important invasive plants in Hungary, pp. 13-33
edited by Zoltán Botta-Dukát and Lajos Balogh
© 2008, Institute of Ecology and Botany, Hungarian Academy of Sciences, Vácrátót, Hungary
14 L. B
A., divided into four sections2. e section Fallopia contains annual plants with climbing stems, such
as copse bindweed (F. dumetorum /L./ J. H) and black bindweed (F. c on v ol v u l us /L./ A. L). e
section Parogonum K . H includes perennial creeping plants, with no representative occurring
in Hungary. Perennial or ligneous plants are categorized in the Sarmentosae (I. G.) H. section,
such as Russian vine (F. baldschuanica /R/ J. H) and silver lace vine (F. a ub e r t ii /L. H/ J.
H).3 e Reynoutria (H.) L. P. R D section contains Japanese knotweed (F. j a p on i -
ca), giant knotweed (F. sachalinensis), and their hybrid the Bohemian or hybrid knotweed (F. ×bohemica).
Due to their synanthropic expansion, invasive and strong habitat-transforming nature, Japanese, giant and
hybrid knotweeds have been in the focus of intensifying scientific and nature conservation scrutiny in the
past 20-25 years. Because the three species are highly similar and because their distribution data are thus
significantly overlapping and unclarified, it seems reasonable to deal with them together. e reason the
authors introduce the three taxa sometimes at different depths is the limitations caused by different levels
of international research into these taxa.
morphology
e three species discussed are robust, herbaceous perennial (geophyte) plants usually taller than a man.
ey have roots penetrating 1-2 m deep down from their base, and far-reaching, laterally spreading rhi-
zomes, bearing buds on them. In the categorization system developed for clonal plants by K et al.
(1997), they belong to the “Aegopodium podagraria”-type. With their dense shoot system budding from
the rhizome, they create connected offshoot colonies (polycormons) which are easily recognized even in
the defoliated stage from the pectinated pattern of erect stems, coloured in dun when dried. eir stems
are upright and thick, hollow at the lower section, and leafless at the bottom. eir leaves are large, broad
or elongated ovate, more or less cuspidate at the apex, with entire margin. Leaf shape and size vary at dif-
ferent life stages and at different locations on the plant. e largest are the ones on the stem, their dispo-
sition being sparse. Ones located on the lateral ramifications are considerably smaller, placed oppositely.
eir flowers are arranged in small glomerules, in multi-axial partial inflorescences with bracts, togeth-
er making up axillary, short-axled complex panicles (pleiothyrsus). In addition to the openly positioned
main inflorescence atop the stem, there are also accessory inflorescences on the leafy paracladia. Func-
tionally, these species are dioecious (sometimes polygamous, with mixed – unisexual and hermaphrodite
– flowers), meaning that there is sexual dimorphism in flower composition and inflorescence structure.
Staminate flowers are 9 mm long, whereas pistillate ones are only 5–6 mm, but the perianth can grow
further on when the fruit is ripened. e five tepals are united at their base, forming a tubelet. e outer
ones have three keels or are winged. e number of stamens is 8, and the stigmae on the 3 free-standing
styles are fimbriated. On functionally male specimens the pistils are reduced, whereas on female plants
stamens are vestigial. F. ×bohemica is an exception, because in this species hermaphrodite flowers (with
fully developed stamens and pistils) can grow on male specimens. No fruit is produced, though, in this
case. However, even fruit can be produced on the staminate (male) specimens of F. sachalinensis, be cause
in this species pistils are only partially reduced. Apart from these exceptions, the enwrapped, three-edged
or three-winged achenes are produced on female (pistil-bearing) flowers only, the fruits measuring about
10 mm. In case of F. japonica, the achene is 2–4 mm long, weighing 1.6 g per 1000 seeds. ese species
bear nectaria as well. eir floral nectaria are of the epithelium-type, whereas extrafloral nectaria located
on the external surface of cicatrices belong to the trichoma and pit types. Further exomorphological fea-
tures used for differentiation between the three species are listed in Table 1. From that it is apparent that
the hybrid F. ×bohemica is located between the parent species (F. japonica and F. sachalinensis) not only
1 B et al. (1995) believe that the Reynoutria sectio of Fallopia genus includes F. japonica together with its varieties, F. ×bo-
hemica and F. sachalinensis, but the category “Japanese knotweeds” describes only F. japonica v ar. japonica and F. ×bohemica.
Later for convenience F. japonica, F. sachalinensis, F. ×bohemica and any backcrosses were referred to collectively as Japanese
knotweed s.l. (cf. B W 2006).
2 is classification was not taken over by Flora Europaea and by the majority of Central-European literature. Instead, these
knotweed species are still dealt with in the genus Reynoutria.
3 e taxonomy (and thus adventive distribution relations) of the two species are not viewed uniformly in international literature.
15Fallopia japonica, F. sachalinensis and F. ×bohemica
in respect of its chromosome number but also in certain morphological features. Phenotypic variability
is mostly characteristic for the highly polymorphic F. japonica, especially in its native range where it re-
mains shorter. However, it is typical of all three species and in all of their habitats that under arid circum-
stances the plants will have shorter stem and smaller leaves. F. sachalinensis is the most similar in size, and
can be clearly confinable species both in its native and adventive range. For quite a long time, infraspecific
taxa have not been described apart form F. japonica, and more recently in F. sachalinensis, from their na-
tive distribution area.4 Besides F. japonica va r. japonica × F. sachalinensis = F. ×bohemica other hybrids are
also known which are considered to be partly intrasectional (belonging to Reynoutria section)5 and part-
ly intersectional taxa (belonging to Reynoutria and Sarmentosae sections)6. e basic chromosome num-
ber typical in species belonging to Reynoutria section is n = 11. e characteristic chromosome number
(2n) of each species are shown on Table 1, but some literature records report different cytotypes (incl.
aneuploids) too, e.g.: F. japonica va r. japonica (2n = 44, ~60**, 66*, 110*),7 F. sachalinensis (2n = 66**, 88**,
102*, 103*, 132*), F. ×bohemica (2n = 88**). e molecular genetic analyses performed in the United King-
dom and in the Czech Republic shows that the order of genotypic variability of these species is the fol-
lowing: F. japonica va r. japonica < F. j . var. compacta < F. sachalinensis < F. ×bohemica, i.e. the hybrid is ge-
netically the most diverse taxon in the study areas (H et al. 1998, M et al. 2005). In
attempts to genetically characterize knotweed species in Britain by molecular markers, including RAPDs
and ISSRs, and to evaluate genotypic diversity in invasive Fallopia germplasm (H B-
2000), a single genotype of F. japonica was detected, suggesting all individuals were ramets of a sin-
gle, but exceptionally widespread clone. e octoploid female (male-sterile) individuals of F. japonica v ar.
japonica investigated by Czech authors proved to be genetically uniform and belongs to the same geno-
type that is present probably in the whole Europe (M et al. 2005). On the other hand, the results of
recent investigations carried out in the USA suggests the presence of intercrossing, segregating hybrids,
and likely introgression between F1 hybrids and F. japonica. is study also shows the first evidence of
bidirectional hybridization between parental taxa in the USA, emphasizing the complex structure of
populations in that region (G et al. 2007). Hybridization and backcrossing within the species of
4 Fallopia japonica var. compacta (H. f.) J. P. B 1989 (syn.: Polygonum cuspidatum var. compactum /J. D. H./ L.
H. B; P. cuspidatum va r. compactum hort.; Reynoutria japonica v ar. compacta /H. f./ M 1941, ead. comb.
B 1972; Polygonum compactum H fil.; P. sieboldii va r. nanum hort.; P. cuspidatum ’Reynoutria’ /sensu N
1978/) is an alpine variety, being smaller and more compact than var. japonica; it is (30–) 50–60 (–100) cm tall, its stem being
less upright; its lateral stems are dark red or reddish maroon; leaves are small (4–7cm), almost round (characteristically as long
as broad), with thick and leathery blade, strongly truncated base, undulate margin, and abruptly cuspidate apex; the flowers in
the compact (–6 cm), non-branching or slightly branching upright panicles are white, carmine or reddish. It is an alpine dwarf
variant native to volcanic ash and scree habitats of Central and North-Japan. One of its forms – f. colorans – is a typical pioneer
plant growing in cushions of several meters wide in the 300-500 m surroundings of active volcano craters. In its synanthropic
range, it has been found growing wild very rarely, only in the British Isles and Czech Republic so far. It is usually grown in
botanical gardens, and only rarely as an ornamental. 2n = 44.
Fallopia japonica var. uzenensis (H) K. Y H O 1997 (syn.: Reynoutria japonica v ar. uzenensis
H) is a variety with hairy leaf underside native to snowy areas of Japan, on the side of the Japanese Sea. It is also a rare
garden plant in Japan and America. 2n = 88.
Fallopia japonica var. hachidyoensis (M) K. Y H O 1997 (syn.: Polygonum hachidyoense
M; P. cuspidatum var. terminale (H) O; Reynoutria japonica var. terminalis H, R. hachidyoensis v ar. ter-
minalis H) is an isolated endemism native to the Izu Isles located near Honshu, bearing larger leaves with waxy shine. It
grows on windy, bare volcanic ashy terrain or lava fields in open tall herb communities. 2n = 44.
Reynoutria japonica var. spectabilis M (syn.: Polygonum cuspidatum v ar. spectabile D N.) grows somewhat smaller
than var. japonica (–1 m). It is also more sensitive, bearing leaves with white variegation or ruddy, marbly shade. In Japan it is
a rare garden plant too. (No synonymous combination shied to Fallopia is known to exist.)
Reynoutria japonica var. variegata M is a rare garden plant in Japan; it has leaves with white and red striping. (No syn-
onymous combination shied to Fallopia is known to exist.)
Fallopia sachalinensis var. intermedia (T.) K. Y H O 1997 (syn.: Polygonum sachalinense var.
intermedium T.).
5 E.g. F. japonica va r. japonica × F. j . va r. compacta, intraspecific hybrid, found in the UK and Germany, 2n = 66; F. japonica × F.
×bohemica (6×), backcross, found in Wales, 2n = 76-110; F. ×bohemica (8×) × F. sachalinensis, backcross, found in Wales, 2n
= 66 (cf. B 2003).
6 E.g. Fallopia conollyana J. P. B 2001 (F. japonica × F. baldschuanica) (cf. B C , B 1992, 2001).
2n = 54.
7 Numbers with a single asterisk refer only to the species’ native distribution area; numbers with two asterisk refer only to the
species’ adventive distribution area.
16 L. B
Fallopia sectio Reynoutria in its adventive range, is clearly a significant and important phenomenon, of-
fering as it does, the possibility of the production of individuals better suited to these non-native regions
(B 2003). is case also render the suggestion by E S (), hybridiza-
tion may act as a stimulus to invasiveness.
T Features of the three member of the species group
Feature
Japanese knotweed
(Fallopia japonica
var. japonica)
Bohemian or
hybrid knotweed
(Fallopia ×bohemica)
Sakhalian or
giant knotweed
(Fallopia sachalinensis)
Height (1.0–) 1.5–2.0 (–3.0) m;
in its native range around
1.5 m (2.0–) 2.5–3.5 (–4.5) m (2.0–) 2.5–3.5 (–4.5) m
Shape of leafs on
middle of stem broadly-ovate, triangular broadly-ovate elongated-ovate
Shape of leaf base truncate or cuneate upper leaves: mostly trun-
cate or cuneate; lower leaves:
slightly cordate
upper leaves slightly cordate,
lower ones definitely cordate
Leaf tip cuspidate, oen curved acuminate, oen curved acuminate or obtuse,
not curved
Leaf size length 5–15 (–18) cm
width 4–10 (–13) cm length 10–23 (–30) cm
width 9–20 (–22) cm length 15–35 (–43) cm
width 10–20 (–27) cm
Leaf texture leathery–stiff intermediate so
Hairiness of leaf
underside
underside appears glabrous,
but with a hand lens, unicel-
lular papillae are slightly vis-
ible sitting on primary veins,
on a swollen base; intervenal
spaces are glabrous
if the underside is bent and
held towards the light, a
hand lens reveals 0,5 mm
long, 1-4-cell stout hairs
(trichomes) sitting on a swol-
len base, mostly on veins;
intervenal spaces are almost
glabrous
the 1 mm long, 4-12-cell flex-
ous hairs (trichomes) sitting
on a non-swollen base, scat-
tered mostly on the veins but
also in intervenal spaces, are
visible to even the naked eye
Position of pistillate
inflorescences
the lateral axles of individual
panicles lack further rami-
fications, and are arranged
loosely, sticking out straight
in all directions
the lateral axles of individual
panicles lack further ramifica-
tions, and are arranged more
densely, sticking out straight,
slightly bent or sometimes
arching downwards
the lateral axles of individual
panicles lack further rami-
fications, and are arranged
more densely, uniformly pen-
dulous
Position of
staminate
inflorescences
the lateral axles of individu-
al panicles may have further
ramifications, and are ar-
ranged loosely and more or
less pointing upwards
the lateral axles of individu-
al panicles may have further
ramifications, and are ar-
ranged densely, forming an
acute angle with the axis of
the main inflorescence, and
pointing up towards the light
in bundles
the lateral axles of individu-
al panicles may have further
ramifications, and are ar-
ranged densely and mostly
upright
Flower biology,
sexual expression
only pistillate (female) speci-
mens are fertile (fruit may be
produced); male specimens
(bearing staminate flowers)
are sterile (no fruit is pro-
duced)
only pistillate (female) speci-
mens are fertile (fruit may be
produced); male specimens
(bearing either staminate or
hermaphrodite flowers) are
sterile (no fruit is produced)
both pistillate (female) and
staminate (male) specimens
may be fertile (fruit may be
produced in both cases)
Number of flowers
in one cluster 2–4 3–5 (–6) 4–7
Position of anthers
in male flowers not exserted from the peri-
anth considerably exserted from
the perianths somewhat exserted from the
perianths
17Fallopia japonica, F. sachalinensis and F. ×bohemica
Feature
Japanese knotweed
(Fallopia japonica
var. japonica)
Bohemian or
hybrid knotweed
(Fallopia ×bohemica)
Sakhalian or
giant knotweed
(Fallopia sachalinensis)
Flowering period July – September July – October July – September
Shape of fruiting
perianth (achene
enclosed in the
persistent perianth)
obcordate, broadly winged
and abruptly narrowed into
the pedicel
elongated-obcordate, broadly
winged and first abruptly,
then run almost parallel
into the pedicel
elongated, narrowly winged
and gradually narrowed into
the pedicel
Width of fruit
(including wings) 3–6 mm 2–4 mm 1.5–3.5 mm
Colour of achene black, shiny bronze, shiny dark purple, shiny
Grown in Hungary ornamental ornamental botanical garden plant
Degree of naturali-
sation in Hungary naturalized, invasive naturalized, invasive, trans-
former casual
Most typical
habitats
in Hungary
survives firstly in areas it was
formerly grown, mostly in
ruderal synanthropic envi-
ronments, or less frequent-
ly in degraded near-natural
habitats
found firstly in degraded
near-natural habitats (pre-
dominantly along rivers and
streams, and in floodlands),
and secondly in ruderal
synanthropic environments
practically absent from ar-
eas outside the places it was
grown
Distribution
in Hungary country-wide, but sporadic found country-wide, being
most common in hilly re-
gions
practically in botanical gar-
dens only
Typical
chromosome
number
2n = 88 (F. j. var. japonica)
[2n = 44 (F. j. var. compacta)]
2n = 66 (F. j. var. japonica /2n
= 88/ × F. s. /2n = 44/)
2n = 44 (F. j. var. compacta
/2n = 44/ × F. s. /2n = 44/)
2n = 44
Identification key for species of the Reynoutria sectio of the genus Fallopia, growing in Hungary
1. a. Leaf blades are stiff leathery, only seldom longer than 15 cm (not longer than 18 cm and not
broader than 13 cm), broadly-ovate, cuspidate at the apex, truncate or cuneate at the base , making leaf
shape appear to be triangular, most strikingly on the lower and middle section of stem. Leaves are near-
ly glabrous, apart from unicellular papillae on primary veins of leaf underside, visible only with a hand
lens. e number of flowers in one cluster is 2–4. Anthers do not exsert from the perianth. e plant
seldom grows taller than 2 m. It is native to Japan, South Sakhalin, Korea, Central Eastern China and
Taiwan; in Hungary it was originally planted as an ornamental and then naturalized. It occurs mostly in
areas it was originally grown, primarily in synanthropic ruderal environments or degraded near-natu-
ral habitats, sporadically country-wide. (Data collected so far usually regards F. ×bohemica.) It is found
in roadside weed communities and ruderal margin vegetation of shaded moist habitats. It is flowering
from July to September.
Fallopia japonica (H.) R D. Japanese knotweed
b. Leaf blades are soer, their length oen exceeding 15 cm (can be longer than 18 cm and broader
than 13 cm); at least the ones on the lower and middle sections of the stem have cordate leaf base; they
are more or less hairy on the underside. e anthers exsert from the perianth. 2–4.5 m tall, more ro-
bust plant
2. a. Leaf blades have so texture, their length can be greater than 30 cm (–43 cm), width can ex-
ceed 22 cm (–27 cm); they are elongated-ovate, acuminate or obtuse, with cordate base. e underside
is hairy – especially on the veins but also in intervenal sections –, well visible to even the naked eye.
Trichomes are 4–12-cellular, approximately 1 mm long. e number of flowers in one cluster is 4–7.
18 L. B
Anthers slightly exsert from the perianth. It is native to South Sakhalin, North and Central Japan; in
Hungary it is almost restricted to botanical gardens (e.g. Vácrátót). (Reports from its growing wild are
mostly about F. ×bohemica.) It is flowering from July to September.
Fallopia sachalinensis (S.) R D. Giant or Sakhalian knotweed
b. is plant is characterized with transitional features of the parent species. e leaves have inter-
mediate texture, they are not longer than 30 cm and not broader than 22 cm, broadly-ovate, acumi-
nate. e base of the upper ones is truncate or cuneate, and the lower ones – most strikingly on the
lower and middle sections of the stem – are slightly cordate. Leaf underside appears to be glabrous to
the naked eye, but, if examined with a hand lens, it has short, sparse hairs mostly on the veins, while
the intervenal spaces are almost hairless. Trichomes are 1–4-cellular, approximately 0.5 mm long. e
number of flowers in one cluster is 3–5(–6). Anthers exsert considerably from the perianth. is plant
is a hybrid of F. japonica and F. sachalinensis, probably having been created in Europe. In Hungary, it
might have been an ornamental some time ago which then escaped and naturalized. e majority of
its populations in Hungary are male-fertile, do not produce seed and are reproducing vegetatively. It
is found country-wide mostly in degraded near-natural areas or, more rarely, in synanthropic ruderal
habitats, especially in hilly regions. It is a spreading, dangerously invasive species, which is apparent-
ly almost ineradicable. It is found in ruderal margin vegetation of shaded moist habitats and roadside
weed communities. It is flowering from July to October.
Fallopia ×bohemica (C & C) J. P. B Hybrid or Bohemian knotweed
origin, disTribuTion
A) e native range of F. japonica is in East-Asia, (from north to south) in Russia (South-Sakhalin,
southern Kuril Isles), in Japan (Honshu, Shikoku and Kyushu; 0-2800m), Korea, Central-Eastern China
(50-2500m) and Taiwan (2400-3800m).8 It is very common in Japan – the most precise data are from
there –, occurring mostly in hilly and montane areas.
Its adventive range extends onto several continents. It was first introduced to Europe in 1823 to a Dutch
botanical garden. Shortly aerwards, it was planted not only as an impressive ornamental, but in some
places it was grown as a productive farmland green forage or in well-lit forests and forest edges it was
grown as forage for game animals. It oen escaped, and then naturalized in several places. By today it has
spread into a significant proportion of Europe, including West,9 Central10 and partly in Southeast Europe.
It is thought to have become naturalized in 99% of the British Isles, and 41% of European areas. It has in-
sular occurrence in Scandinavia (up to 70° northern latitude), in the Baltic states, Ukraine and Russia11. In
South Europe it is practically absent from the Iberian, the Apennine and the Greek peninsulas.12 Besides
Europe, it has naturalized throughout North-America,13 from Alaska to Georgia, and it still continues to
expand. ere have been reports on its occurrence in Australia and New Zealand as well.14 As regards its
altitude tolerance, in Europe it is considered to be a plant of colline or lower mountain regions not ex-
panding to higher elevations: Scandinavian mountains (–480 m), South Wales (–320 m), Swiss Alps (–800
m, sometimes 1460–1650 m), Baden-Württemberg (90–1000 m), Erzgebirge (–900 m), Krkonose (Giant
Mountains) (–750 m), Tatra (–860 m). North America: California (–1000 m), Utah (1220–1830 m). Only
va r. japonica has become naturalized. From Britain and the Czech Republic only a single female clone has
been known. Currently, F. japonica is widespread in all countries of the Carpathian Basin, although no
data are known from Serbia. e first information about its wild occurrence in the region (1923; cf. P-
8 Altitude limits of distribution are given in parentheses.
9 It was introduced into the United Kingdom in 1825, and it was first recorded as having escaped in 1886.
10 It was introduced into Germany in 1825, and it was first recorded as having escaped in 1884. It was brought into what is now
the Czech Republic in 1892.
11 In Moscow’s wider surroundings, in the Caucasus region, and in Vladivostok in the Far East.
12 But it occurs in the Mediterranean region of France.
13 USA and Canada; it first naturalized in the 1880s in the northeast states of the US.
14 First in 1935.
19Fallopia japonica, F. sachalinensis and F. ×bohemica
1957) was reported in general by J (1924), and its subspontaneous occurrence was first record-
ed by K F. along Tisza river at Óbecse (S 1927). About a quarter of a century later, already 18 Hun-
garian settlements were listed (P and S in S 1952). Its occurrence data have increased since
then, especially in the most recent decade. According to U (1973) – although it has sporadically
established in the Great Hungarian Plain region –, it has become frequent in the middle-altitude mountain
range and in Transdanubia, expanding most strongly in the latter regions (S 1980). P (1985)
considers it to have become completely naturalized, found almost everywhere throughout the country.
However, the author of the current study believes, based on observations having been made for more than
one and a half decade that this plant is much less frequent as reported in literature, because many of these
reports probably relate to the hybrid species (B 1998).
B) e native range of F. sachalinensis is also East Asia: it is native to Russia (South Sakhalin, south-
ern Kuril Islands), northern (Hokkaido) and central (northern sections and central part of the western
side of Honshu; 0–1050 m) areas of Japan, being a relatively frequent plant there. (Occurrence and dis-
tribution data of infraspecific taxa of the above two species are listed in the section of morphology.)
Its adventive range is narrower than that of the congener species, but it also extends onto several of
the continents. It was introduced into Europe in 1863: first into the Royal Botanical Garden in Lon-
don, and into the Moscow Zoo. Like in the case of the former species, this one, too – although more
rarely – was planted as an ornamental and as forage. It has naturalized in several parts of Europe, but
has remained much more sporadic. e focus of its distribution is Northeast Europe15 and the north-
ern part of Central Europe16. South of 45° northern latitude there are only Bulgarian occurrence data.
It has other insular occurrence patches in the south of Scandinavia (up to 65° northern latitude), in the
Baltic countries, in Ukraine and in Russia17. Shortly aer its introduction to Europe it was imported to
North America too, and from the middle of the 20th century it has had subspontaneous occurrence data
(California, eastern-central parts of the USA). It was first reported from New Zealand in 1936, from
Australia (Victoria) in 1954, from South Africa (Natal) in 1987 and from India in 2000. As regards its
altitude preference, in Europe it is thought to be a species of colline and submontane regions: Scandi-
navian mountains (–250 m), Baden-Württemberg (90–710 m), Giant Mountains (Krkonose) (–750 m,
on Polica: –895 m); in North America: California (–500 m). From the Carpathian Basin there are only
some sporadic occurrences in Austria, Slovakia and Romania. ere are only few reports on its wild
occurrence in Hungary (the first one: Vácrátót 1949 in P 1957; P 1985). It is probably
that these data concern about hybrid species that were still not described at that time but were similar
in many respects. Until today, its occurrence has been proved only as a planted, botanical garden pant
(e.g. Vácrátót)18, and only in the most recent times was founded its small stand in the Gerecse hills (Vé-
rtestolna, B 2006).
C) Surprisingly the hybrid between F. japonica and F. sachalinensis was not mentioned from Japan
until 1997, when Reynoutria ×mizushimae Yokouchi ex T. Shimizu was described. Its possible reason is
that F. japonica and F. sachalinensis are either not sympatric or if and where they are, any hybrid proge-
ny is poorly adapted. B (2003) found several examples of F. ×bohemica growing in ruderal habitats
in NW Honshu in 1999 and 2000 (all were hexaploid, indicating a cross between octoploid F. japonica
and tetraploid F. sachalinensis). Apparently these hybridizations were a result of the practice of planting
F. japonica along new roadside embankments and cuttings for soil-stabilization purposes. In Europe F.
×bohemica was created probably spontaneously as a hybrid between the above two species. It was dis-
covered in 1982 in Northern Bohemia and described in 1983 by C and C. Its distribu-
tion was studied in only few of the countries. According to such research, it has naturalized in Belgium,
15 It was introduced into the United Kingdom in 1860, and it was first recorded as having escaped in 1896.
16 It was introduced into Germany in 1863 and into what is now the Czech Republic in 1869.
17 In Moscow’s wider surroundings. First date of its introduction: 1864.
18 Botanical Garden of the Hungarian Academy of Sciences: Developmental History and Phytotaxonomy Garden, Polygonaceae
plot. However, escaped populations along the stream Sződ-Rákos flowing in the Botanical Garden are not F. sachalinensis.
20 L. B
British Isles, Bulgaria, Czech Republic, Denmark, Finland, France,19 Germany, Hungary, Italy, Nether-
lands, Norway, Poland, Romania, Serbia,20 Slovakia, Switzerland and Ukraine, but most likely in other
countries as well.21 Available records range from 67° in the North to 43° (latitude) in the South and from
10° in the West to 25° in the East (longitude). Outside Europe it has been reported to occur in the USA,
Australia and New Zealand also. It is probably cultivated and probably also escaped in China. As to the
latitudes, European data are available from Norway only: Scandinavian mountains (–250 m). In Hunga-
ry it is mostly the functionally male specimens or populations of the hybrid knotweed, usually not pro-
ducing fruit that are seen. In Hungary, where it is the most frequent among the three species it has con-
tinued to expand considerably in recent times too. To conclude, the synanthropic range of these three
species, including their Hungarian distribution, is most probably expanding and becoming denser.
life cycle
e life cycles and life histories of the three knotweed species – due to their high similarity – can be dealt
with together, with the important differences being specified. ey are probably the tallest polycarpic
(flowering several times) perennial herbaceous plants of the Hungarian flora (apart from liana species).
Being geophytes, it is their extensive, lignescent rhizomes that over-winter. In the native ranges of the
parent species – especially as pioneer species of volcanic terrain – an effective generative way of repro-
duction has vital importance.22 However, this is not true in their synanthropic ranges and in the case of
the hybrid species. As experience shows, the adventive “career” of these species is most likely to be rely-
ing primarily on their effective vegetative reproduction ability. e efficiency is so high that these plants
were studied in the 1980s as the general empirical model of vegetative plant growth.23 During the au-
tumn and winter period, over-wintering buds are generated on the base of the stem and on the lignify-
ing rhizome, to produce new shoots in spring, among which the strongest are the ones emerging on the
crown of the stem base. Rapid shoot development starts at around late March – early April, depending
on the weather. Young shoots might suffer damage from late spring frosts. According to French data, F.
sachalinensis grows in the first three weeks at a rate of 3 cm/day; this rate increases to 5 cm/day by the
third week of May. As the season proceeds, the densely positioned stems with lignified base, developing
from the robust rhizomes, will become suberous on their lower sections. Later on, lateral ramifications
will also develop, thus multiplying total leaf surface of the plant. By that time, however, leaves of the main
stem become yellow, and then fall. Inflorescences start to develop as early as in June. e formation of
functionally dioecious flowers is accompanied by the less intense development and retardation of the ad-
equate parts of the hermaphrodite archaic flowers. Flowering normally starts in the second half of July,
reaching its maximum in August when the plants are the tallest, and lasts until September–October, al-
though plants that are injured can produce flowers and continue flowering until the first frosts. Flowers
are predominantly insect-pollinated (entomogamous). e most frequent visitors of flowers, floral and
extrafloral nectaria are dipterans (Diptera), especially syrphid flies (Syrphidae) and muscid flies (Musci-
dae). Also common are hymenopterans (Hymenoptera), beetles (Coleoptera), Rhynchota and moths and
butterflies (Lepidoptera). If fruits are produced, they will ripen by around September–October, and are
dropped in October–November. Earlier frosts can damage the abscission mechanism in the appropriate
zone of the fruit pedicel, with the result that the fruits stay on the plant way into the winter season, un-
til weather or the birds remove them. eir winged achene fruits are wind-dispersed (anemochorous).
19 In the Mediterranean region too.
20 Data from K. S (pers. comm.)
21 Investigations to clarify actual occurrence data of the parent species and their hybrids in various areas are currently under
way.
22 Germination happens above ground (epigeic), meaning that it is the stem section below the cotyledons (hypocotyl) that ex-
tends, rising up the cotyledons. When F. japonica seeds were investigated, dormancy was broken even at room temperature,
but germination rate was then very low.
23 Recently published a correlated random model for the spatial spread of a rhizome network in F. japonica, which is able to the
practical application in forecasting future disposal costs of existing stands (S et al. 2008).
21Fallopia japonica, F. sachalinensis and F. ×bohemica
In Europe, however, instead of generative reproduction, they spread almost entirely vegetatively.24 ere
are very few evidential data on generative reproduction (i.e. on plant specimens germinating and grow-
ing up under natural conditions). ere are data of seedlings from Germany on the F. ×bohemica hybrid
between F. japonica and F. sachalinensis (A 1998), and from the British Isles on the F. × co n ol -
lyana hybrid between F. japonica and F. baldschuanica.25 Studies in the USA were proved, while clonal
growth is apparent, there is more evidence for sexual reproduction (F K 2003, G
et al. 2007). Germination experiments conducted in Belgium (T et al. 2007) were showed that F.
japonica produced large quantities of seeds that had germination capacity, but in contrast to the Ameri-
can studies, they did not observed any seedlings in the field. e high occurrence of adult hybrids in the
study area and the observation that there is high genotypic diversity in these hybrids (T et al. 2007),
similar to that observed in Britain (H et al. 1998), indicated that seedling establishment
does occur in the field, albeit probably at a low percentage in comparison to the total seed rain. Further
experiments are needed to assess the best conditions for hybrid seedling establishment. e major dis-
persers of the reproductive parts (rhizome or sometimes stem sections) suitable for the development of
a new individual are humans and water. ese parts are usually transported away from their growing lo-
cations by human mediation (anthropochory), e.g. with garden waste, etc. If it getting to edaphically arid
or ruderal habitats their populations usually become stable and gradually expand. From moist, waterside
habitats, their – mostly vegetative – propagules are transported further by flowing waters (hydrochory).
In addition to the fact that the size of the ligneous stem base (serving as a regenerative complex) grows
with time, laterally expanding rhizomes with regenerative buds also develop even in the first year. ese
can cover a distance of as far as 15–20 m from the plant (of course, depending on soil compactness). e
three knotweed species discussed are sensitive to prolonged dry spells during summer. Leaves fall from
late October, or aer the first frosts at latest (they are sensitive to frost early in the autumn), causing the
stem to die off too. Regeneration ability is the most important characteristic for spreading in the species
of Fallopia sectio Reynoutria. e regeneration rate and shoot mass were significantly affected by geno-
type in F. ×bohemica but not in F. sachalinensis (P et al. 2003). Some phenotypes of F. ×bohemica
exhibit high regeneration potential and the hybrid can be considered as the most successful representa-
tive of the genus Fallopia sectio Reynoutria in terms of regeneration and establishment of new shoots. F.
sachalinensis shows the lowest regeneration ability. e regeneration from stems is less efficient than that
from rhizomes except F. sachalinensis. It could be concluded that rhizomes are more crucial than stems
for the spread of knotweeds through fragmentation and clonal growth, suggesting the importance of soil
disturbance (B et al. 2003). e examination for a variety of ecological and genetic parameters of
some F. ×bohemica populations in north-eastern France (S et al. 2008) indicates that some
clones are more aggressive than others with a similar chromosome composition. Aggressiveness can be
linked to the absence of seed production and possession of large leaves, which might allow higher stor-
age of nutrients and greater volume of rhizome in the soil. It is illustrative to the differences in the viabil-
ity of these species that during the last century in the Czech Republic F. japonica v ar. japonica has been
spreading significantly faster than F. sachalinensis and the hybrid exhibits twice the rate of invasion of its
parents (M et al. 2004).
habiTaT preference
Autecology
e distribution area of the parent species, including their Hungarian and synanthropic ranges, is limited
to areas characterized with the following climatic features. Relatively wet summers, regular frost (F. sacha-
linensis: 120 days below 0 °C mean temperature; F. japonica: at least one shorter period below 0 °C mean
temperature), long and mild vegetation period (about 210 days above 5 °C mean temperature), except for
F. japonica occurrence in Northeast Utah (USA) where the summer is too dry. While the entire distribu-
24 e role of F. japonica and F. sachalinensis fruits in the expansion of these species needs to be clarified in further studies.
25 Cf. the footnote in the part of morphology referring the hybrids.
22 L. B
tion range of F. sachalinensis is limited to the temperate phytogeographic zone and sub-oceanic regions,
that of F. japonica includes the sub-meridional–temperate zone and a wider area of oceanic regions: from
oceanic to subcontinental. For this reason , no significant expansion of distributions is expe cted in t heir an-
thropogenic range – unless in the case of climate change –, although it is likely that occurrence frequencies
will increase. It is remarkable the progressive spread of F. ×bohemica (and the absence of F. japonica) in the
mesomediterranean zone of southern France. F. ×bohemica seems to exhibit an ecological ability that is –
contrary to its morphology and physiology – not intermediate between its parents, but reveals new quali-
ties of independent niche adaptation and range widening (B W 2006).
A) F. japonica has wide ecological amplitude. In its native range it is usually found in higher altitudes
than its congener species. For example, its dwarf variety (F. japonica var. compacta) is one of the most typ-
ical plant species of open, sunny spots of new ash or lava surfaces in volcanic mountains (e.g. Fuji). is
variety produce large amounts of seed, which regularly germinate, and the plants appear to grow as dis-
crete circular stands with little evidence of lateral spread. e rhizomes grow straight down rather than
laterally (B 2003). However the most typical habitat for the tall F. japonica v ar. japonica in Japan
are edge of the forests or riversides in forests, on poor, fast-drying, gravely soils with bad water balance.
Secondary it is frequent along roads, managed pastures too, especially where high nitrogen-level fertil-
izers are used. It oen occurs not in compact stands, but as single well-separated stems, which had long
rhizomes relatively close to the surface (B 2003). It can tolerate extraordinarily harsh environmen-
tal conditions (e.g. its rhizomes withstand months of frozen soil, and survives on extremely acid volcanic
soils (< pH 4). With low absorption values, it also tolerates high sulphur-dioxide pollution present near
active volcanic fumaroles. Its extensive rhizome system stabilizes moving stone debris. Being a plant that
stores nitrogen and other important nutrients, it assists the development of soil, the establishment of oth-
er species, and increases the chances for the development of a more highly organized ecosystem.
In its adventive range, F. japonica occurs in various, relatively productive, usually man-made habitats
with oen disadvantageous features, which can be divided into three groups based on their edaphic char-
acteristics. e first group contains more typically man-made, relatively dry areas or those with ill water-
balance, which are partly pioneer habitats: railway embankments, waste heaps, empty yards, neglected or
abandoned gardens, hedges, ruderal areas, roadsides, etc. e second group, on the contrary, comprises
more near-natural, moister areas: areas along regulated (sometimes unregulated) streams and rivers, em-
bankments and dykes, roadside ditches, forest edges, clear-cut sites, etc. e third main habitat type of its
occurrence is sea coasts (e.g. Norway, Denmark) and salt marshes. All this indicates that indirect and di-
rect disturbance can assist its expansion. e fact that its populations belonging to the first type group are
concentrated in the close surroundings of human settlements is most probably related with its ornamen-
tal uses, with the effects of human soil disturbance, and with the rarer late autumn frosts and summer
droughts. is species has wide pH-tolerance (3.0–8.5), but normally prefers limy soils. It is not choosy as
regards soil type, and tolerates high levels of heavy metal and salt pollution. In North American investi-
gations on F. japonica and F. ×bohemica were proved that plasticity in salt tolerance traits may allow these
taxa to live in saline habitats without specific adaptation to tolerate salt (R et al. 2008). Some-
what contradictorily with its Hungarian name (“floodplain Japanese knotweed”), this plant in Hungary
is found primarily (as observed by the author) in places where it escaped from its former planting sites,
mostly in settlements’ ruderal habitats, or sometimes in degraded near-natural habitat types. us, in
Hungary it is rather urbanophilous species. According to G et al. (1988) it has competitor strategy.
B) In its original distribution F. sachalinensis lives in forest edges, along forest trails, on scree habi-
tats of montane areas, on seaside rocks, riversides, abandoned lands and along public roads. Generally,
it prefers alluvial lowlands with higher temperature, lower elevation and constant water supply in the
vegetative season. However, sometimes – similarly to the other species – it does occur as a pioneer colo-
nizer of recently formed bare volcanic surfaces, or along alpine gullies and flowing waters.
In its adventive range F. sachalinensis is present in the first two major habitat groups mentioned
above for the congener species. However, the occupancy rates of warmer and dryer ruderal habitats
23Fallopia japonica, F. sachalinensis and F. ×bohemica
in urban areas vs. wetter and colder habitats of mountainous areas vary highly and characteristically
among areas within Europe. For example, in Poland it is known from forests mostly, whereas in France
it is typically found on vast alluvial lowlands and islands of alpine rivers.
C) e habitats of F. ×bohemica, known so far from Europe, belong to three groups on the basis of
edaphic features, similarly to the case of F. japonica.26 e author has found it to be an urbano-neutral
species in Hungary, although it is present primarily in degraded moist, near-natural areas (along rivers,
streams of hills and mountains, floodplains, sometimes along intensively used forest trails, and only sec-
ondly in more strongly anthropogenic, ruderal habitats. It favors highly exposed situations with no cov-
erage, but can appear in shaded forest areas too in which case its stands appear to be less dense.
Phytosociology
A) In its native range F. japonica is a pioneer species of riversides and shallows: the Polygonum cuspida-
tum association (Penniseto-Artemision principis, Artemisietea principis) is a 40-100 cm high, relatively
species-poor one, characterized with the dominance of the name-giving species. It is found in other –
mostly tall herb – associations too, where vegetation is somewhat higher (50–150 cm). It plays an im-
portant role in the succession of volcanic surfaces where it is a constituent of natural pioneer plant as-
sociations. During succession it is normally grass patches of Miscanthus sinensis that accompany this
knotweed species, then, aer about 50 years, this grass will become dominant with other grass species,
to be followed by woody vegetation in the habitat.
In its adventive range, F. japonica (just like the two other species) has very low sociability. In the ma-
jority of cases it forms more or less continuous, homogeneous stands. For this reason, phytosociological
literature treats these as associations signified by the name of the species only, or just as stands (F. j a po n -
ica association, F. japonica stands). However, it can be additionally specified what types of associations
these stands co-occur with. According to more recent Central-European literature (N et al. 1993,
O M 1994) these are: willow and alder bushes, montane alder galleries along streams
(Stellario-Alnetum, S.-Petasitetum), garlic mustard (Alliarion), burdock (Arction lappae) and sweet clover
associations (Dauco-Melilotion). Applying the derived association concept which was first used about 25
years ago – and which focuses on the dominating species – Japanese knotweed tall herb associations are
also differentiated (Fallopia japonica-Senecion fluviatilis) (M et al. 1993), comprising the F. j a po n i -
ca extreme facies of the Impatienti-Solidaginetum association and the Polygonetum cuspidati association.
In the diagnostic species combination with dominant and constant accompanying species, the dominant
species is F. japonica, whereas stinging nettle (Urtica dioica), bishop’s goatweed (Aegopodium podagrar-
ia) and stickywilly (Galium aparine) are subdominant species. e latter are tolerant of shading; Urtica
and Aegopodium are tough clonal plants. Coenosystematically, F. japonica has been classified in various
association units, for example in Germany S (1962): Senecion fluviatilis, O & M
(1983): Galio-Urticenea; in the Czech Republic H & S (1990): Convolvuletalia sepium and La-
mio albi-Chenopodietalia boni-henrici. According to S (1970), Japanese knotweed in Hungary is typi-
cally found in gallery forests, oak woods (Quercetum petraeae-cerris), floodplain weed associations (Cus-
cuto-Calystegietum), forest edges and gardens; and is considered to be a Calystegion sepium species and
a character species of alluvial weed associations (Senecion fluviatilis) . B (1995), too, classifies it as
a Calystegion sepium species, but according to S (2000) it is a Calystegietalia-type species, which is
validly called today (B S 1999) Convolvuletalia sepium (moist, edge vegetation). e lat-
ter authors categorize all three species as new, floristically incomplete and unbalanced neophyte associa-
tion elements of semi-arid and moist forest weed vegetation types. All these categorizations mentioned
above provide a view of the phytosociological character of F. japonica.
B) In its original distribution, F. sachalinensis can be characterized with the following major veg-
etation-typical features. Firstly, it is a member of the so-called giant herb communities, that forms of
26 Cf. also with the establishment respecting the salt tolerance of F. japonica.
24 L. B
1.5-3 m height and nearly 100% coverage (Angelico-Polygonetum sachalinensis, Cirsio kamtschatici-
Polygonetum sachalinensis) occurring in forest edges, mountain terrain covered with rocky debris, sea-
side rocks and riversides. Secondly – similarly to the congener species –, it is one of the first colonizer
species of newly formed volcanic terrain surfaces, establishing themselves in such areas within the ini-
tial couple of years.27 Later on, trees that gradually settle in depending on knotweed density will shade
out knotweed populations from such habitats within a few decades. Its almost homogeneous stands are
found making up the pioneer vegetation of newly formed barren surfaces in human settlements.
In its adventive range the phytosociological characteristics of F. sachalinensis – just like its habitats –
are similar to those of F. japonica, although exact phytosociological data are deficient. O &
M (1983) regard it as a Galio-Urticenea species, H S (1990) as Convolvuletalia sepium
and Lamio albi-Chenopodietalia boni-henrici species, whereas L S (1992) relate it with
associations of moist forest weed associations along streams (Aegopodion), and, as an epecophyte, with
associations of ruderal habitats. B S (1999) treat it together with the other two knot-
weed species, although valuable data are not available from Hungary.
C) e phytosociological relations of F. ×bohemica have been less studied in Europe. However, a con-
siderable proportion of such data on F. japonica are probably about the hybrid species. Nevertheless, the
occurrence preferences of the hybrid in Hungary (described earlier in the section on habitats) seem to be
valid in this respect, too, and are thought by the author to be unlike those typical of F. japonica. According-
ly, it is most frequent in ruderal margin associations of rather near-natural, shaded and moist habitats (Ga-
lio-Urticetea), more specifically, in vegetation types characterized with alluvial weed associations (Senecion
fluviatilis).28 If all Hungarian populations are regarded, its proportions in highly anthropogenic roadside
weed vegetation (Artemisietea vulgaris) have only secondary importance. It can be noted that already some
populations growing in beech forests are known to exist. Communities dominated by F. ×bohemica re-
corded in the Mediterranean Sea (France) characterized by thermophilic species, which composition typi-
cal of the (meso-) Mediterranean region, especially at riparian sites (B W 2006).
bioTic inTeracTions
Allelopathy
Japanese knotweed species show a typical example of allelopathic mechanisms which are among the
most effective means of competition between plants. Reynoutriin was separated from F. japonica leaves
(Q-3-xyloside), whereas terpenoid: triterpene (sterol), phenoloid: tannin, flavonoid (quercetin glc), and
anthrachinone (emodin) compounds were found in F. sachalinensis. e results of American experi-
ments suggest that allelopathic interference or interaction with microbial soil organisms may contribute
to the lack of native species in populations of F. ×bohemica (S B 2007).
Competition
Although in the adventive range, knotweeds have little in the way of competition from plants other than
trees, in their native range (Japan) they must additionally cope with climbers, twiners and other mem-
bers of the native giant herb communities. Even the commonly found grass, Miscanthus sinensis grows up
to 2 m in height, parasitic Cuscuta taxa are strong enough to bring down the plants and Pueraria lobata
with its vigorous smothering growth and Wisteria with its dense tangling growth provide worthy com-
petition (B 2003). In the same time an interesting indicator of Japanese knotweed toughness and
vitality is the fact that among species of species poor communities of areas depleted by the falling guano
of cormorant (Phalacrocorax carbo) nesting colonies in Japan, the highest surviving coverage is made up
by F. japonica (I 1996).
27 Owing to its strong ability to produce offshoots, it is capable of emerging from below 0.5-1.0 m thick volcanic sediment, rap-
idly creating dense stands, and regenerating older colonies buried under the sediment.
28 Here it oen co-occurs with other alien, invasive tall herbs or lianas, such as adventive Aster species, Echinocystis lobata, Helianth us
tuberosus s.l., Humulus japonicus, Impatiens glandulifera, Parthenocissus inserta, Rudbeckia laciniata or Solidago gigantea.
25Fallopia japonica, F. sachalinensis and F. ×bohemica
In their adventive range, in addition to allelopathic effects, the success of these three knotweed spe-
cies is ensured by other important features such as shading and subterraneous nutrient depletion. With
their early-starting and rapidly proceeding growth they occupy the air space before other species could
develop, by shading them off gradually with their dense stems and foliage mass, eventually taking away
almost all the available light. In addition, their rhizome system grows rampantly, and the plants inten-
sively remove the nutrients from the soil, thus taking over the ground, too, from their competitors. All
these together, result in an almost 100% inhibition of germination and growth in co-occurring species.
ere are only few exceptions from this, mostly plants growing and producing fruit in the early spring
period (e.g. Ficaria verna, Veronica hederifolia). It is only a few liana species that sometimes are able to
overcome its aggressive, monodominant stands, such as Clematis vitalba, Humulus lupulus, Echinocystis
lobata or Calystegia sepium. Investigating the stands of the three Fallopia species along a north Bohe-
mian river the authors concluded that the species richness of communities has no influence on the suc-
cess of Fallopia invasion; the combination of environmental conditions and propagule spread is more
important to the invasion success than the number of species in the host community. Fallopia inva-
sion greatly reduces species diversity.29 F. japonica invaded more habitat types than F. sachalinensis and
F. ×bohemica. e hybrid F. ×bohemica out-competes the parental taxa at sites where both taxa occur
(B et al. 2004). American researchers used a factorial transplant experiment to assess whether
light limitation, nutrient limitation, or allelopathic interference by Fallopia ×bohemica reduces growth
or survival of two native species. e results in combination with the outcome of a cutting experiment
suggest that F. ×bohemica achieves competitive superiority primarily by limiting access to light. Species-
specific effects and significant interaction effects particularly of light and activated carbon suggest ad-
ditional mechanisms (S B 2007).
Herbivores
A) e highest amount of data is available on F. japonica. In Japan its leaves were consumed by chry-
somelid beetles which could reduce them to a delicate tracery of veins as well as various lepidopteran
and sawfly larvae. Upper stems frequently bore the exit holes of stem boring larvae. Below ground, the
large larvae of the Japanese swi moth (Endoclita excrescens) bored cylindrical holes through the thick
rhizomes, and their damage and old exit holes were a common feature of knotweed rhizomes in Japan.
Another herbivore the Asian longhorn beetle (Anoplophora glabripennis). Beyond these the aphid in-
festations and various rust infections decrease the leaf area (B 2003). Its herbivores known from
Europe are the followings: mammals: in the British Isles, the epigeous shoots were grazed by sheep,
cattle, goats, horses and donkeys. Rhizomes however are toxic to some farm animals. Grazing by sheep
and cattle early in the summer had a significant negative effect on shoot density. Birds: house spar-
rows (Passer domesticus) were observed to feed on seeds. Acarids: Tetranychus urticae (Tetranychi-
dae). Insects: only very few insect herbivores were identified on Japanese knotweeds; this may be one
of the reasons for the success of knotweeds discussed; Butterflies and moths (Lepidoptera): Spilarctia
lutea, Spilosoma lubricipeda (Arctiidae), Apatele megacephala (Caradrinidae), Phlogophora meticulosa
(Noctuidae), Taeniocampa gothica, Orthosia circellaris (Orthosiidae), Inachis io (Nymphalidae), and
other larvae belonging to the families Noctuidae and Geometridae, not having been identified so far;
Beetles (Coleoptera): Phyllobius pyri, Otiorhynchus sulcatus (Curculionidae), Gastroidea (Gastrophy-
za) viridula, Chrysolina fastuosa (Chrysomelidae). Neither endoparasitic nor ectoparasitic nematodes
have been found.
B) Data are deficient in the case of F. sachalinensis. One polyphagous moth (Spilarctia lutea, Arc-
tiidae) and one aphid was found on this knotweed species in Europe (Germany). Spilarctia lutea was
equally successful on this knotweed and on its original native host plant Rumex obtusifolius. It is an in-
teresting aspect to this topic that this knotweed species (and maybe the other two as well) attract ants
with their extrafloral nectaria, possibly increasing protection against insect herbivores.
29 Similar results have been found by Hungarian authors too (B & B-D 2007).
26 L. B
C) Data on herbivores feeding on F. ×bohemica are available from Germany only. Moths (Lepi-
doptera): Spilarctia lutea (Arctiidae). Beetles (Coleoptera): Gastroidea (Gastrophyza) viridula (Chry-
somelidae). Dipterans (Diptera): Pegomya nigritarsis (Anthomyidae). Undetermined acarid species are
also observed. Gastroidea (Gastrophyza) viridula had only 15% growth compared with its individuals
feeding on their native host plant Rumex obtusifolius.
Pathogens
A) In case of F. japonica, no parasitic fungi have been found. Among pathogenic saprophytic fungi, the
following have been identified. Ascomycotina: Amphorula sachalinensis (Great Britain), Ceriospora po-
lygonacearum (Great Britain), Chaetoconis polygonii (Great Britain), Cytospora polygoni-seiboldi (Great
Britain), Glomerella cingulata (Japan), Myxosporium polygoni (Great Britain), Pezizella effugiens. Basidi-
omycotina: Puccinia phragmitis (Japan), Puccinia polygoni-amphibii (Japan), Puccinia polygoni-weyrichii
(Japan). Deuteromycotina: Alternaria sp. (Germany), Cladosporium sp. (Japan), Colletotrichum gloeo-
sporioides (Great Britain), Endophragmia cesatii (Germany), Epicoccum sp. (Germany.), Fusarium sp.
(Japan), Helminthosporium sp. (Japan), Phoma spp. (Great Britain, Japan, Germany) incl. Phoma anceps
va r. polygoni and Ph. polygonorum, Phomopsis polygonorum. Further sixteen plurivorous microfungi
have been reported from growing and dead stems.
B) In F. sachalinensis the following saprophytic fungi have been identified: Ascomycotina: Ceriospora
polygonacearum, Myxosporium polygoni; Deuteromycotina: Phomopsis polygonorum, Phoma polygono-
rum.
C) No data are available for F. ×bohemica.
Symbiosis
No mycorrhiza was found when samples from F. japonica in the British Isles and F. sachalinensis in Po-
land were investigated.
economic imporTance
Benefits
Due to their rapid growth resembling that of bamboo species, F. japonica and F. sachalinensis have been
planted as ornamentals for quite long, especially in the lawn of gardens and parks, and on watersides.
Because of the high protein content of their leaves, experiments were made for their cultivation as for-
age for domestic and game animals.
A) Several medicinal uses of F. japonica are known to exist.30 In addition to that, there are also some
ethnobotanical uses as well: for example World War II troops used its leaves as tobacco. Young shoots are
said to have been used for salads, because their taste resembles that of almonds. If cooked, it is suitable
for dishes prepared similarly to asparagus or as puree. It can also be used as a substitute for rhubarb, to be
accompanied by a specially prepared sour sauce. Recently, its utilization for purifying soils contaminated
by heavy metals was also suggested, because it can accumulate those metals in its leaves and stem.
B) F. sachalinensis used to be popular among German hunters because it was hypothesized that it is
tastier for game animals than F. japonica, and it also seemed suitable for lurking during hunting. In Rus-
30 In traditional Japanese and Chinese medicine, its dried rhizomes are recommended for curing the following diseases: pu-
rulent dermatitis, gonorrhoea, favus, Dermatophyton mycosis and hyperlipemia. Some probable agents have been shown by
K et al. (1983). One of the acting agents (resveratrol) is thought to have bactericidal and fungicidal impact, which had a
reducing effect of cholesterol level in rats. e extracted drug called emodin had an inhibiting effect on the intestinal parasitic
trematode Schistosoma japonicum. e active drug content of this species used in Chinese medicine also for healing burns was
analyzed by M (1991) (partly supported by S L. Gy.).
27Fallopia japonica, F. sachalinensis and F. ×bohemica
sia, it was used as silage too.31 In its native range, sometimes there are so many larvae living in the inter-
nodal sections of the stem that they are oen used by anglers as a source of bait. Its rhizome is thought
to be suitable for curing a number of diseases; the active drugs are anthrachinone-derivatives. In some
places of Japan its young and tender shoots are eaten. In Europe, recently it has been discovered that it
is effective against fungal plant diseases. e extract made from its leaves proved to be suitable against
mildew on apple, begonia, cucumber, wheat, and the botrytis of sweet pepper. In hot climates, its huge
leaves are used for shading fruits in the market.
C) By taking advantage (not actively growing!) of the functionally male, non-fruiting F. ×bohemica
stands, utilization ways similar to those of the parent species could be revealed: food, medicine, pesti-
cides, purification of heavy metal contaminated soils, stabilization of waste heaps, etc.
Damages
F. sachalinensis was recommended in the USA for stabilizing embankments on riversides, but this later
proved to be unwise, because wherever it was used for such purpose, its spreading went uncontrolla-
ble. It is also possible, although actually no such information have arisen yet, that F. japonica was also
planted in Europe some time for the same purpose. ese three knotweeds (incl. F. ×bohemica) are
less recommended today for being used even as garden ornamental plants. High standard gardening
books ornamental plant and botanical garden catalogues (index seminum) nowadays particularly call
the attention to the difficulties and threat meant by the escaping and control of this (and similar inva-
sive) species. Knotweed stands, spreading along flowing water bodies, cause problems in accessibility,
flow rate, and increase the maintenance costs of regulated river sections, by damaging flood preven-
tion engineering objects. In settlement environment they can damage traffic infrastructure: crack side-
walk surfaces, or can even penetrate through weaker paved roads. ey can suppress plants and hedges
planted in parks, along roads and watersides. Fortunately, they only very seldom appear as weeds in
agricultural areas. In California, for example, both species are considered as harmful weeds, F. sacha-
linensis “forming densely infested areas” (H 1993). However, it is not specified in the literature
source mentioned whether these plants cause “only” nature conservation problems or they are also an
agricultural weed.
naTure conservaTion significance
Although such problems caused by these knotweed species are not new ones, the attention of nature
conservation organizations has turned towards them only recently.32 With their expanding polycor-
mons they form almost entirely homogeneous stands in which only few species appear occasionally,
but even so the majority of these species are unable to reach generative stage. rough direct or indi-
rect human mediation, they can establish well in natural or near-natural habitats as well or even spread
there, depending on the vegetation type affected there. In the invaded areas they strongly inhibit natu-
ral succession and regeneration processes and spontaneous reforestation, but also drastically reduce the
survival chances of herbaceous associations. By excluding members of the original flora and vegetation
in the habitat, they reduce the biodiversity of plants, and through that, of animals too, and thus are det-
rimental to biodiversity in general. eir control is very difficult, and any intervention with chemicals
brings about nature conservation concerns. For these reasons – although these knotweed species occur
in a variety of habitats – the most problematic from the aspect of nature conservation is their expansion
in near-natural, waterside habitats.
31 e first piece of such data is from 1864.
32 Occasionally, warnings have been released, for example the United States Department of Agriculture called the attention to
the rampant, aggressive spreading ability of F. sachalinensis as early as in the late 19th century.
28 L. B
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Web reference
JKLIST: JAPANESE-KNOTWEED JISCmail list (e Japanese Knotweed Forum).
<http://www.jiscmail.ac.uk>
