I'll follow up my original post by asking if anyone is aware of any specimens growing at gardens or arboreta in the Pacific NW? This species was sometimes listed under another genus previously (Kalopanax, Acanthopanax, Eleutherococcus).
Very few gardens worldwide have this in their collections: https://www.bgci.org/plant_search.php Unfortunately, the search results do not reveal the names of the gardens.
I believe there are a couple arboreta on the east coast (USNA for one) that have young specimens, but I haven't heard of any mature trees in North America. Because it is used as a spring vegetable in Japan, I was thinking someone on the west coast (where there are relatively large Japanese communities) might be more familiar with it, and possibly even growing it.
