The wingnut in the Belfast Botanic Gardens was in the process of re-growing from a stump and was not flowering when we first photographed it in 2010. It may be the Caucasian wingnut, Pterocarya fraxinifolia or the hybrid wingnut, Pterocarya x rehderiana. When it flowers once again this could be resolved.

The wingnuts are very vigorous trees, mostly from China with one species from Japan and one from the south of the Caspian Sea. The leaves are compound and resemble those of ash (Fraxinus) and walnut (Juglans) the latter being in the same family as the wingnut. A feature of wingnuts, shared with walnuts, is that the pith in young stems is segmented as shown in the photo below. They are prolific sucker producers and a single tree can quickly spread into a clump many metres across, as the splendid example near the lake in Rowallane Garden shows. Suckers can be controlled if the trees are grown in grass which is kept mown as can be seen in Edinburgh Botanic Garden.

NOTE 2019: The Pteriocarya in Belfast is now more than twice the size it was in 2010 and is flowering prolifically. There is still some uncertainty about the identification, but it appears to be more like P. fraxinifolia

Photos taken in Belfast Botanic Gardens and Edinburgh Botanic Garden in 2010 and Belfast Botanic Gardens in 2023. Copyright: Friends of Belfast Botanic Gardens.