Table 1 Morphological characteristics of knotweed species based on literature review^3,11,12,13.

Leaf shape and size

Broadly ovate-triangular, 5–18 cm long, 4–13 cm wide; typically up to 15 cm long and 10 cm wide

Intermediate between R. japonica and R. sachalinensis; typically broadly ovate, 10–27 cm long, 9–22 cm wide; typically up to 23 cm long and 20 cm wide

Broadly oblong-ovate, heart-shaped or elongated, 15–43 cm long and 10-27

 cm wide; typically up to 40 cm long and 25 cm wide length: width ratio c. 1.5

Leaf base

Acuminate/ ovate/ nearly truncate/ truncate/ bluntly wedge-shaped narrowed

Sagittate or moderately cordate; typically base bluntly wedge-shaped (upper leaves) or slightly cordate (lower leaves)

Deeply cordate

Leaf apex/tip

Pointed, cuspidate or

acuminate, narrowed into a long tip, curved intermediate

Intermediate, variable pointed, slightly acuminate

Acute, tapering to obtuse/ rounded/ bluntly pointed

Leaf trichomes

Sparse (few to none), short, on leaf underside along veins, reduced to short, single-celled papillae with a strongly swollen base mostly glabrous or scabrous to tuburculate (type A)

Sparse, intermediate trichome shape, density, and length; short,

1-4-celled, with a strongly thickened base (type B)

Dense, longer hairs on leaf underside, 1–5 cells, and 8 or greater (type C)

Stem features

Hollow, green with reddish/purplish/brown speckles and reddish nodes, bamboo-like, up to 2–3 m tall; grow in groups of several to a dozen from a rhizome node (shoot clump)

Variable, often faintly speckled, intermediate height, typically up to 3,5 m; grow in groups of several to a dozen from a rhizome node (shoot clump)

Hollow, robust, usually without speckles, up to 4–4,5 m tall; grow singly or in groups from a rhizome node (shoot clump)

Growth habit

Dense, bamboo-like thickets, upright growth

Combines the dense formation of R. japonica with the spreading nature of R. sachalinensis

Less dense thickets, spreading growth habit