FREI, J. 2021. A BRIEF HISTORY OF JUGLANDACEAE. ARNOLDIA, 78(3): 10-17 
A Brief History of Juglandaceae 
Jonas Frei 
hen I first encountered butternuts on 
the ground of the arboretum here in 
Zurich, Switzerland, I was puzzled. 
The tree these nuts fell from must have died 
or been felled years ago, so I only had the seeds 
for identification. This North American spe- 
cies, Juglans cinerea, is rarely seen in European 
cultivation outside specialized tree collections, 
and I didn’t recognize the ridged, oblong nuts. 
When I took a few home, they were not easy to 
identify within books on common park trees. 
After additional research, however, the butter- 
nut aroused my fascination and left me with 
questions about the whole walnut family (Jug- 
landaceae). I had long been familiar with this 
group of plants, but the more I read about them, 
the more I realized that, in fact, I knew so little. 
Like the butternut, many other members of 
the walnut family were absent in books that 
I had at home: hickories (Carya), wingnuts 
(Pterocarya), and platycarya (Platycarya). As I 
encountered each new species, new questions 
arose. After several years of intensive study, 
my pursuit evolved into a book project, Die 
Walnuss, which was published (in a German 
edition) in late 2019. My work with this unique 
plant family went far beyond scientific analy- 
sis; it also involved an artistic exploration of 
the unique variety of forms of this plant fam- 
ily. I wanted to make the knowledge hidden in 
scientific papers accessible through a language 
of drawings and photographs. These differ- 
ent approaches—science and art—offered new 
ways of observing and understanding the world 
of walnuts. 
_ 
I live in a region with no native species of this 
widespread plant family. Here, you can occa- 
sionally find the North American eastern black 
walnut (Juglans nigra) planted as an ornamental 
tree in parks. The English walnut (Juglans regia) 
was most likely introduced by the Romans into 
the northern parts of Europe and can often be 
found growing as lone specimens on farms. But 
the number of these solitary trees has declined 
in the region since the industrialization of agri- 
culture half a century ago. Walnut farms and 
orchards are relatively new in the German- 
speaking part of Europe, and walnuts bought 
in grocery stores here mostly originate from 
France (Périgord and Grenoble}, the United 
States (California), or Chile. 
Members of Juglandaceae, however, were 
once among the most common trees of allu- 
vial forests in Central Europe. Fossils allow us 
to look back on a plant family whose greatest 
diversity and distribution preceded the ice ages 
in the Paleogene and Neogene. Many species 
disappeared only a few hundred thousand years 
ago. I became fascinated by this history. The 
fossil record reveals a long, slow story of evo- 
lution and shifting ranges, and it provides a 
counterpoint to the story of the family’s rapid 
globalization in recent centuries. 
Not far from Strasbourg, in the Rhine Val- 
ley of France, researchers and fossil collectors 
have discovered fossilized butternuts, described 
under the name of Juglans bergomensis. These 
fossils correspond so closely to the North 
American butternut that it is hard to find 
visual differences. The nuts must have fallen 
into the shallow water and sandy substrate of 
the Rhine five million years ago, but they still 
have almost the weight and feel of fresh nuts 
due to carbonization. In fact, this species had a 
wide distribution: its fossils have been reported 
in Italy, the Netherlands, and wider parts 
of eastern Europe and Russia. Similar fossils 
dating to the Neogene have been found in 
Japan and in the southern United States. Fossil- 
ized hickory nuts are also present in the Rhine 
sediments, including those of a widespread 
fossil taxon called Carya globosa, which is sim- 
ilar in appearance to the water hickory (Carya 
aquatica). Although all the European hickory 
species went extinct millions of years ago, 
Facing page: The walnut family is best known for nut-bearing species like the English walnut (Juglans regia), pictured 
here in the Thur Valley of Switzerland, but the family also includes notable wind-dispersed species. 
ALL IMAGES BY THE AUTHOR 
