The winged fruits of Pterocarya macroptera maturing in summer. (Photo by Niall Dunne)
BY CHRISTINA PFEIFFER
Quietly tucked away in the Arboretum’s old field nursery, on the south side of Crabapple Meadow, a stately specimen of Pterocarya macroptera holds court amid a group of other remnant nursery trees. The sight of this tree, draped in its long chains of rounded, large-winged seed pods in late summer never fails to strike me with awe.
The wingnuts (Pterocarya) are a small genus (just six species) of deciduous trees native to floodplains and moist forests in Asia and parts of Europe. They belong to the walnut family (Juglandaceae) and share similar pinnate foliage structure with their walnut (Juglans) cousins: Each of their large, “feather-like” compound leaves are made up of numerous small leaflets.
Graceful Shade Tree
Wingnuts are monoecious, meaning they produce separate male and female flowers on the same plant. These arrive in spring in the form of dangling catkins bearing tiny, wind-pollinated flowers. The female catkins then develop over several months into long, showy, pendulous chains of seedpods (botanically “nutlets”) with prominent wings. The wings help disperse the seeds via wind and—for trees growing alongside rivers—water.
The large-winged wingnut’s “walnut-like” compound foliage. (Photo by Niall Dunne)
A few of the wingnut species are relatively common in cultivation and also can be seen in the Arboretum: Caucasian wingnut (Pterocarya fraxinifolia), Japanese wingnut (P. rhoifolia), and Chinese wingnut (P. stenoptera). An easy one to find is the huge specimen of Chinese wingnut growing beside two shagbark hickories (also members of the walnut family) along Azalea Way, just south of the Woodland Garden. In summer, it produces lovely, long chains of nutlets with linear wings.
Best suited for sizable gardens and large sites in the landscape, wingnuts quickly grow to the stature of large shade trees, well over 60 feet tall. They are valued for their graceful form and tolerance of wet soils. The furrowed bark on mature specimens is also an attractive feature; on Pterocarya macroptera, it is light-greyish brown with longitudinal striations.
Fragmented Populations
Pterocarya macroptera is less common in cultivation and is also a conservation concern in its home range of central China, where it grows in river valleys and by mountain streams. As of 2019, it has been listed as “vulnerable” on the International Union for Conservation of Nature Red List of Threatened Species (iucnredlist.org). Threats include habitat fragmentation caused by urban development and agriculture.
Close-up of the female (left) and male flowers (right) in spring. (Photo by Niall Dunne)
Only 120 scattered wild populations of the species are known, and these are all fairly small, comprising fewer than 50 trees each. Large-winged wingnuts are typically found sparsely intermingled amid other forest trees, and regeneration from seed is low. Scientists are studying the species’ genetics and trying to develop proactive management measures to ensure the survival of the existing stands.
Pterocarya macroptera is a relict species, tracing back to fossil records, and these records show that its distribution was once much more widespread. Botanists have also identified three natural varieties (Pterocarya macroptera var. macroptera, P. macroptera var. delavayi, and P. macroptera var. insignis), but these can be difficult to tell apart, and the subdivisions need more study.
The species name translates to “large wing,” from the Greek makros, meaning “large,” and pteron, meaning “wing.” The name is well earned because the wings on each elliptical seedpod can grow up to three centimeters wide—a centimeter wider than the nut wings of the next widest wingnut, P. rhoifolia.
Close-up of the striated bark. (Photo by Niall Dunne)
In the Arboretum
Growing off the beaten path, amid a mixed cast of other trees from the old field nursery, the Arboretum’s lone specimen of the rare large-winged wingnut is something of a rarity within the collection itself. (The 50-foot tree is not hard to locate: It is just east of the large cluster of Chinese flowering quince, Chaenomeles cathayensis, on the east side of Arboretum Drive as you walk uphill from the Woodland Garden to the Magnolia Collection.)
UW Botanic Gardens Curator Ray Larson says that the specimen’s origins are from seed collected in the far eastern part of Shaanxi Province by the Arboretum of the Chinese Academy of Forestry in Beijing. The seed was then sent to the University of British Columbia Botanical Garden, germinated, and given to Washington Park Arboretum in 1981 as a three-foot-tall specimen. The Arboretum has tried, on different occasions, to propagate the plant from cuttings, but so far, the attempts have not been successful.
“It’s a lovely species,” says Ray. “And hopefully we can try again at some point.”
Cultivating threatened species in botanic gardens can help preserve their genetics, as well as build awareness about the plight of the plants and the urgent need for their conservation. Hopefully, fostering the large-winged wingnut will enhance its presence in our minds, our gardens, and the wild.
Christina Pfeiffer is a horticulture educator and author with more than 40 years of experience. She teaches regular classes at the Center for Urban Horticulture and is also a member of the “Bulletin” Editorial Board.
References
Wang, T-R. et al. “Adaptive divergence and genetic vulnerability of relict species under climate change: a case study of Pterocarya macroptera.” “Annals of Botany” 132: 241–254, 2023.
Kozlowski G. et al. “Wingnuts (Pterocarya) and Walnut Family. Relict Trees: Linking the Past, Present and Future.” Natural History Museum Fribourg, Switzerland, 2018.
Sutton, J. (2019). “Pterocarya macroptera.” International Dendrology Society Trees and Shrubs Online.
Shot of the full specimen in the Arboretum in mid-summer. (Photo by Niall Dunne)
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This article is reprinted from the summer 2026 issue of the Arboretum Bulletin, our quarterly botanical and horticultural magazine. Published since 1937, the Bulletin is a benefit of Arboretum Foundation membership and features in-depth articles on the Arboretum collections and history, as well as general information of interest to plant lovers in the Pacific Northwest and beyond. Join/subscribe today.
