Fallopia
japonica (Houtt.) Ronse Decraene
Standardized Common
Name: Japanese Knotweed
Other Common Names: Giant Knotweed, Hu
Zhang, Japanese Fleeceflower
Family: Polygonaceae
Taxonomy: The nomenclature of
this species is complicated. In the United States, it is usually called Polygonum
cuspidatum Sieb. & Zucc. As most broadly defined, Polygonum
includes about 200 species, which are distributed nearly worldwide and
frequently weedy. A number of these are found in commerce, often termed
knotweeds, bistorts or fleeceflowers. This group is commonly divided into
several smaller and less variable genera, in which case “P. cuspidatum”
is placed in Fallopia or in Reynoutria as R. japonica
Houtt. The latter is the oldest name for the species, but the epithet “japonicum”
could not be used when the species was included in Polygonum because the
name P. japonicum had already been used for another species. Polygonum
cuspidatum Sieb. & Zucc. is likewise an illegitimate name because that
name had previously been used for another plant, so it appears that there is
currently no correct name for this species when it is placed in Polygonum.
However, the recognition of several genera within this group is well supported
and is to be encouraged. Fallopia japonica is native to Asia but
widespread elsewhere as a weed, or cultivated as an ornamental or for its high
resveratrol content. The plant is dioecious (with the sexes on separate plants)
and the weedy populations in Europe and North America are all female clones,
reproducing asexually through dispersal of rhizome fragments. Hybridization
with F. sachalinensis (F. Schmidt ex Maxim.) Ronse Decraene or F.
baldschuanica (Regel) Holub is common.
Description: Rhizomatous
perennial herb; stems numerous and dense, erect, usually 1–3 m high, sturdy,
branched above, somewhat waxy, often red- or purple-spotted. Leaves alternate, ovate
to broadly elliptic, 5–12(–15) cm long, somewhat leathery; petiole short with
small sheath (ocrea) wrapping around stem; base truncate or occasionally
rounded or broadly cuneate; apex short-acuminate or cuspidate to acute; margins
entire. Plants dioecious; inflorescences lateral, paniculate, 3–12 cm long,
main branches arising near base; flowers numerous, small, in clusters of 2–4.
Perianth of 5 tepals, the outer 3 winged in female flowers, white to greenish
or rarely reddish in cultivated plants; stamens 8, extended from perianth;
ovary 1, with 3 styles and fringed stigmas; vestigial sterile stamens or ovary
present in female or male flowers respectively. Fruit an achene, 3-sided, 4–5
mm long, dark brown to blackish, glossy.
Parts
in Commerce:
Rhizome with roots
Identification:
- Cylindrical,
long, usually cut into short sections or slices, 0.5–2.5(–3.5) cm in
diameter, sometimes irregularly shaped
- Outer surface
brown to grayish brown, longitudinally wrinkled, with small rootlet scars
- Cut surfaces yellowish
to orangish brown
- Fracture hard
- In
cross-section, contains thin brown cork; narrow ring of yellowish to tan
or pale brown cortex and phloem; broad ring of yellowish wood with
numerous thin, irregular rays; small brownish or hollow pith
- Bark can often
be separated from wood
- Pith hollow or
scalariform (containing pale septa that separate darker or hollow
segments, giving “ladderlike” appearance in longitudinal or diagonal
slices)
- Taste weakly
bitter and astringent
Fallopia
multiflora (Thunb.)
K. Haraldson:
The most popular related species is F. multiflora (Fo-Ti or He Shou Wu),
which is usually called Polygonum multiflorum Thunb. in the United
States. The large, irregularly shaped, woody root tubers can be up to 15 cm
long and 12 cm in diameter, and are cut into chunks or slices before drying.
The outer surface is reddish brown to nearly black, irregularly grooved, with
transverse lenticels. The cut surfaces are yellowish to reddish brown. The
fracture is hard and starchy; some tubers are very woody at the center. The
phloem is relatively thick and in each tuber contains several abnormal vascular
bundles, which are nearly round and have been described as “forming brocaded
patterns.” The taste is weakly bitter, but includes some sweetness.
References:
Hollingsworth ML, Bailey JP, Hollingsworth PM,
Ferris C. Chloroplast DNA variation and hybridization between invasive
populations of Japanese knotweed and giant knotweed (Fallopia,
Polygonaceae). Bot J Linn Soc. 1999;129:139–154.
Li A, Park C-W. Reynoutria. In: Wu Z, Raven
PH, Hong D, eds. Flora of China, vol. 5. Beijing: Science Press and St.
Louis, MO: Missouri Botanical Garden Press; 2003:319.
Pharmacopoeia Commission
of PRC, eds. Pharmacopoeia of the People’s Republic of China, English ed., vol. 1. Beijing: Chemical
Industry Press; 1997:202 [and pp. 163–164 for Fo-Ti].
Ronse Decraene L-P, Akeroyd JR. Generic limits in Polygonum
and related genera (Polygonaceae) on the basis of floral characters. Bot J
Linn Soc. 1988;98:321–371.
Webb DA. Reynoutria. In: Tutin TG, Heywood VH, Burges NA, et al.,
eds. Flora Europaea. 2nd ed., vol. 1. Cambridge:
Cambridge University Press; 1993:47
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