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Walnut, Juglans regia (Juglandaceae)

I am fond of nibbling on walnuts and shelling them. This may be a cultural legacy: as my name shows, I am of Hungarian descent and Hungary was for centuries a major center of walnut production.

Where did the walnut tree Juglans regia originate, when was it domesticated by mankind and why is it that eating its nuts can be health-beneficial? Those are some of the topics in this note.

Walnut trees are found all over the planet, due primarily to the numerous uses for the wood of this tree and to the nutritional benefits from its seed, the walnut. Half the world production comes from China. In the US, the Central Valley of California is another major
center of walnut production. However, the pressures of environmental degradation and climate change through drought, salt, and spring frost, are gradually reducing walnut yields
Juglandaceae greatest diversity and distribution preceded the ice ages in the Paleogene and Neogene. The walnut came to China from its presumed origins on the Iranian Plateau via trade and human migration along the Land Silk Road. Yet, the Qinghai-
Tibet Plateau in southwestern China (including southern Asia and southwestern China) may be the core region of genetic diversity.

Scientists mapping both walnut forests and languages have discovered close relationships between the two along the major Silk Road routes. Travelers along the trade routes were planting forests as long-term food supplies. Human-mediated admixture between Anatolian and Balkan walnut germplasm started in the Early Bronze Age, and between western Europe and the Balkans in eastern Europe during the Roman Empire. Indeed, the name Juglans means, in Latin, Jupiter’s acorn, testifying to its highly nutritive qualities.

The Pannonian basin (modern Hungary and Slovakia) became a crossroads of European cultures, promoting contacts and hybridization between walnut genetic lineages from western Europe and the Balkans. Subsequently, after the decline of the western Roman Empire (1,600 before the present (BP) and tumultuous Migration Period (1,700–1,100 BP), and as a consequence of urban development and increasing human population density, the Late Middle Ages (900–500 BP) marked a favorable period for fruit cultivation and agriculture in Hungary and its adjacent regions, leading to a local walnut population expansion.

The current lengthening of life expectancy brings about increased incidence of old- age infirmities, such as memory loss and Alzheimer syndrome. Which points to the health benefits of walnuts. Walnuts contain bioactive peptides with demonstrated neuroprotective
effects, making them a valuable ingredient in food. Laboratory studies on rats showed that maternal feeding with walnuts improves learning and memory in their adult pups. Human
clinical trials have also suggested an association of walnut consumption with better cognitive performance and improvement in memory when compared to baseline in adults. As a reminder, my personal cue is the uncanny resemblance between a walnut, in its bipartite and folded appearance, and a human brain!

We are indebted to Jonas Frei, an architect in Zürich, for drawings of walnut shells from various species, origins and times (including fossils from riverbeds), that display their beauty (Arnoldia, 2021, 78(3)).

Published inPlants