Japanese walnut is a large spreading deciduous tree that grows up to 15 metres tall.
Description
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Leaves are 60cm long with long petioles (stalks).
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Leaflets in groups of 9-17 are usually hairless above and densely hairy below.
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Single male catkins hang from stems, females are on erect spikes with purple hairs.
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Flowers are red/pink/purple and visible between October-November.
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Fruit is sticky and clustered, covered in down and rust coloured.
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Seed are thick-shelled nuts dispersed by water, dumped vegetation, and possum/pigs/rodents.
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Habitats include riparian margins, wetlands, roadsides, scrub, disturbed forest, grasslands, and drainage channels.
What you need to know
Japanese walnut forms dense stands, excluding native vegetation. Allelopathic.
Management approach
Japanese walnut is declared an unwanted organism by the Ministry for Primary Industries (MPI) because it is capable of causing harm to the natural environment, physical resources or human health in Aotearoa/New Zealand.
These species pose a high risk to our environment, economy, recreation, and cultural values.
Rules
Any species declared a pest, including unwanted organisms, cannot be sold or be in a place where plants are being sold. Pest plants cannot be propagated, bred, or multiplied, communicated, released, or cause to be released, or otherwise spread.
Control
Do not attempt to undertake control of Japanese walnut yourself. Report any sightings to us.
Male flowers (catkins). Photo credit: Trevor James
Fruit is sticky and covered in down. Photo credit: Trevor James
Female flowers. Photo credit: Trevor James
