16 Arnoldia 78/3 « February 2021 
cea, which was described in 1843. Some bota- 
nists initially thought it was a conifer due to 
its cone-like fruiting structures. In 1844, the 
famous English plant collector Robert Fortune 
also found Platycarya in China. Assuming that 
it was a new, not-yet-described species, he sent 
herbarium material and seeds to the Royal Hor- 
ticultural Society in London. John Lindley, the 
secretary of the society, named the plant after 
its finder, Fortunaea chinensis, and called the 
species the most important new find of For- 
tune. Later, it became known that Siebold had 
described the species one year earlier, so today 
the name Fortunaea is only used as a synonym. 
These scientific explorations—and those of 
other botanists—made it possible to describe, 
collect, and, of course, cultivate many of the 
species as ornamentals and orchard trees. But 
this era of Siebold and Fortune was not sim- 
ply a time of great scientific discovery; it was 
also a time of European colonization, in which 
the gathering of knowledge on expeditions was 
often combined with ideological, cultural, and 
religious imperialism. This movement of plants 
around the world coincided with violations 
of ethical standards by European maritime pow- 
ers and a merciless approach to other cultures. 
The relatively slow but efficient distribution 
of Juglandaceae by squirrels and mice seems 
innocent in comparison. 
—_ 
When the walnut family is viewed in the broad 
sweep of its evolutionary history, the speed of 
its recent spread is clearly unprecedented. As 
beautiful as it is to see the worldwide diversity 
of Juglandaceae close together in many parks 
today, the globalization of the family has also 
produced novel threats. 
As humans moved the walnut family around 
the world, fungi and pathogens often migrated 
with the species. In the United States, a fungal 
disease known as the butternut canker (Siro- 
coccus Clavigignenti-juglandacearum) has 
brought the butternut to the brink of disap- 
pearance. The fungus, which was once native 
to Asian walnut species, causes little damage 
to its original hosts, but it is often fatal to the 
North American butternut. The thousand can- 
kers disease, meanwhile, is the result of the 
unfortunate encounter of a fungus (Geosmithia 
morbida) and a beetle (Pityophthorus juglandis) 
that formed in the western United States due 
to the proximity of the eastern black walnuts, 
cultivated in parks, and natural populations of 
the Arizona walnut (Juglans major). And the 
walnut fruit fly (Rhagoletis completa), which 
once lived inconspicuously on the black wal- 
nut species of North America, today spreads 
quickly in walnut orchards of Europe. 
Meanwhile, the close planting of related 
Juglandaceae species leads to the formation of 
hybrid offspring. This has led to major changes 
in natural environments, especially in the case 
of the butternut populations in North America. 
Many of the butternut trees that can resist the 
butternut canker also carry the genetic material 
of Japanese walnuts (Juglans ailantifolia). Resis- 
tant hybrids have greater fitness, as they sur- 
vive and have more offspring, which could be a 
blessing for the American butternut stocks that 
survive the strong fungal infestation. On the 
other hand, conservation of the “real” butter- 
nut becomes more complicated. This scenario 
reveals the cascade of unintended but profound 
environmental consequences of human actions, 
which cannot be easily resolved. 
Of course, the walnut family experienced 
various climatic changes over the past fifty mil- 
lion years and therefore changed its distribution 
again and again. It is assumed that many of the 
species we know today are the result of hybrid- 
ization between different populations that col- 
lided after a long separation due to climatic 
fluctuations and subsequent spread by squirrels 
and ravens. Genetic studies suggest that the 
English walnut originated from the hybridiza- 
tion of the black walnuts (section Rhysocaryon) 
and Asian butternuts (section Cardiocaryon). 
Also, the American butternut is said to carry 
some black walnut genes in addition to the 
genetic material of similar Asian species from 
the Cardiocaryon section. Given this history, 
one could say that many walnuts, as a lineage, 
will adapt to human-made influences, although 
it is unlikely all of the walnut species we know 
today will survive the pressure. 
_ 
Recently, in a second-hand bookstore, I found 
a small booklet titled Die Quaianlagen von 
Zurich, from 1889. The author, botanist Carl 
Joseph Schroter, planned the tree collection at 
the arboretum where I first encountered the 
