The Japanese ash is a form of Manchurian ash growing naturally on the northern Japanese islands of Honshu and Hokkaido, as well as on Sakhalin Island. On the cool mountain slopes it tends to concentrate in moist sites at the edges of mires or along rivers, with conifer forest dominating drier sites. Highly valued for the attractive patterning of its timber, the Japanese ash has become rather rare in the wild because of over-exploitation.
It seems that the only external characteristic differentiating the Japanese from the Manchurian ash is the greater hairiness of the leaf undersides. Being from a maritime climate it is probably better suited to the fluctuations of the Finnish climate than the Manchurian form. However, because it tends to break leaf very early, it is best planted in cool, permanently moist sites under a protective tree canopy. Resembling the native ash (F. excelsior), the Japanese ash flowers early before leaf flush, the flowers themselves being easy to miss. The typical ash keys develop in bunches on female trees, persisting into late autumn.