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Pterocarya stenoptera - Chinese wingnut

During the Eocene, 50 million years ago, the wingnuts (Pterocarya) grew as forests throughout the whole of the northern hemisphere, but nowadays they are limited to Asia. However, they seem to be making something of a come-back in Finnish gardens.

The wingnuts are fast-growing, often with multiple trunks, and their dangling flower catkins can grow to half a metre. The common name derives from the seeds, which develop as small winged nutlets. The leaves are large, made up of opposite leaflets resembling those of the ash (Fraxinus), and turn a beautiful yellow in autumn.

The Chinese wingnut grows naturally throughout China except for the far north. The leaves are smaller than the other wingnut species; the central leaf rib is often grooved with two serrated flanges or wings, at least for part of its length. The species has thrived at Mustila since 1999, and may be slightly less susceptible to frost damage than other wingnut species.


Pterocarya rhoifolia - Japanese wingnut


The wingnuts belong to the walnut (Juglandaceae) family; they have showy ash-like leaves and long hanging fruit catkins, to which the winged nuts are attached. The amount of edible nut in the wingnuts is about the same as that in the seed of the Scots pine (Pinus sylvestris), i.e. not much; in this they differ completely from their cousins, such as the English walnut (Juglans regia) or the pecan (Carya illinoensis). Nevertheless the hanging decorative catkins give the tree a distinctive appearance in late summer. The catkins turn brown in autumn and remain on the tree long after leaf fall.

There are eight Asian species in the genus, and the Japanese wingnut is one of the hardiest. However, it is susceptible to spring frosts, which turn the leaves black. Japanese wingnut enjoys rich moist deep soil. In southern Finland it also seems to thrive in moist clay soils. The trees do best in protected spots in parks and gardens, for example against building walls, at the forest edge and especially by water.


Pterocarya fraxinifolia - Caucasian wingnut

The wingnuts (Pterocarya) are large deciduous monoecious trees (i.e. male and female flowers in the same tree) whose dangling inflorescences develop into fruit catkins up to half a metre long. The name comes from the decorative winged nuts. This particular species, the Caucasian wingnut, has grown in earlier periods of warmer climate in Europe but has had to retreat to its present habitat in the river valleys around the Caspian Sea. It was taken into cultivation in western Europe at the end of the 1700s.

This is the handsomest of the wingnuts which can be grown successfully in Finland, with large compound leaves of opposite leaflets. Unfortunately the provenance of the seed cultivated in nurseries is hopelessly tender in Finnish winters. Plants from Uppsala have grown to over 20 metres in the Djurbäck Arboretum in Inkoo, southern Finland, in only a few decades. It seems that to thrive, seed must be of suitable provenance and the soil rich and moist, with protection from late spring frosts.

The Caucasian wingnut closely resembles the Japanese. A good way to distinguish between the two is the scales protecting the buds: in the Caucasian they are completely absent; in the Japanese they fall during the winter.


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