T.E.R:R.A.I.N - Taranaki Educational Resource: Research, Analysis and Information Network

Juglans ailantifolia (Japanese walnut)

Kingdom:   Plantae
(unranked):  Angiosperms
(unranked):  Eudicots
(unranked):  Rosids
Order:  Fagales
Family:  Juglandaceae
Genus:  Juglans
Species:  J. ailantifolia
Binomial name: Juglans ailantifolia
Synonyms:  Juglans cordiformis, Juglans sieboldiana, Juglans mandshurica var. sachalinensis
Common name: Japanese walnut

Juglans ailantifolia is an invasive tree species of walnut native to Japan and Sakhalin. It is a weed pest as its nuts can be spread by water, by people dumping nuts and possibly by pigs or possums. It inhabits coastal areas, river terraces, roadsides, shrublands, wasteland and old homesteads in the North Island. The nuts are favoured by rats.
As this tree very invasive and 
has now been banned in New Zealand after it was listed as invasive species. It is now illegal under the Biosecurity Act to propagate, distribute or sell this plant - either casually or through nurseries - but existing plants are still allowed on private properties. 

Juglans ailantifolia is a wide spreading deciduous tree (> 20 m tall). Its trunk is >80 cm in diameter and has a light grey bark.The yellow-green leaves are pinnate, >60 cm long, with 11-17 leaflets, each leaflet 7–16 cm long and 3–5 cm broad. They are usually hairless above, densely hairy on veins below and with sparsely serrated edges.
The yellow-green male catkins (<15 cm long) hang from stems during spring, the same time as the new leaves appear.
The hairy female inflorescences (9-22 flowers) are on erect spikes and have a large ovary, small green petals and pink/ red stigmas. These are followed by rust-coloured fruit (25-40 mm) containing hard, rough, thick-shelled nuts which are attached to >4 cm racemes.

Photographed roadside east of Taihape  

A female inflorescence

The yellow-green male catkins


Thanks to Wikipedia for text and information: https://creativecommons.org/licenses/by-sa/3.0/