Reynoutria japonica (Japanese knotweed)

Leaf type: Oval, broadly lanceolate, rounded, heart-shaped at the base
Leaf margin: Smooth
Phyllotaxis: Alternate
Colour: Green, green with red stems
Life cycle: Perennial

Leaf (upper side)

Reynoutria japonica young leaves — Young leaves emerging in the spring.

leaves alternate Reynoutria japonica — The leaves of Reynoutria japonica are arranged alternately along the shoots.

leaves in fall Reynoutria japonica — Reynoutria japonica in October. New leaves and shoots can continue to grow until the first frost.

Growth habit & biology

Reynoutria japonica habitus — A stand of Reynoutria japonica just under three meters tall in front of a wall.

Japanese knotweed (Reynoutria japonica) is a perennial herbaceous plant that can grow up to four meters tall and spreads via rhizomes. It forms dense stands and grows until the first frost.

The leaves are oval, broadly lanceolate, or rounded, with heart-shaped endings. Young shoots are sometimes reddish in color.

shoots Reynoutria japonica — The shoots may be reddish or green in color.

growth habit in spring Reynoutria japonica — As early as May, Reynoutria japonica can be over two meters tall.

Distribution & habitates

Reynoutria japonica is native to East Asia and is considered an invasive species in many regions, where it is being controlled (source).

It colonizes sunny to partially shaded sites and can be found on embankments, along roadsides, in forests, meadows, on riverbanks, and on slopes.

Reynoutria japonica wayside — Reynoutria japonica by a wayside.

Botany

Reynoutria japonica, also known as Japanese knotweed or Asian knotweed, is better known by its botanical synonym, Fallopia japonica. Its common names indicate that it belongs to the knotweed family (Polygonaceae).

Leaf (upper side)

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