The leaves and friable soil slipped beneath us as we climbed—hand over hand—up the slope, careful not to send more boulders ricocheting down the hillside. Luckily, our team was spread out in a near horizontal line, all wearing safety helmets in case more wayward rocks came tumbling down (they did). The bullseye above us was a series of gray-to-orange barked trees, camouflaged against the backdrop: Japanese stewartia (Stewartia pseudocamellia). Although the species is common in cultivation, accessions of documented Japanese provenance are relatively rare within garden and arboretum collections. Thus, we found ourselves in this mesic forest near Chichibu, Saitama Prefecture, Japan, joined by Morris Arboretum’s Anthony Aiello and Polly Hill Arboretum’s Todd Rounsaville (Polly Hill and the Arnold Arboreta both hold Nationally Accredited™ stewartia collections). Our visit to this rocky slope is part of a broader expedition (12–28 September, 2018) that focuses upon Japan’s temperate woody flora, particularly those species of high conservation and research value, and is supported by the Plant Collecting Collaborative (PCC), of which our three arboreta are members.
Our in-country colleagues are Utsunomiya University Professor of Forestry Mineaki Aizawa and his graduate student Tatsuhiko Shibano, both incredible field botanists and consummate caretakers. Armed with our target list of high-priority species, they have led us through forests supporting these and other charismatic plants. Japan’s plant diversity is astounding, luring Arboretum explorers here for some 125 years. This long-term relationship has left a memorable mark: plants of Japanese provenance rank third within the Arboretum’s living collections (behind the United States and China), with 11% of our accessions hailing from the country. Our last expedition to Japan, however, was in 1977—some 41 years ago—and it has been wonderful to finally return as part of the Arboretum’s Campaign for the Living Collections.
The maples in Japan are as gorgeous as they are plentiful, and so far we have made collections from nine separate species, including the endangered Miyabe maple (Acer miyabei) from a population just discovered a few years ago. Two species each of beech (Fagus), hemlock (Tsuga), and fir (Abies) are also in the tally, as well as quite a few exemplars from the shrub layer. These include three species of hydrangea, five rhododendrons, and the unusual Elliottia paniculata, an Ericaceous (heather family) species held in fewer than ten gardens on Earth. Oh, and let’s not forget the Japanese stewartia—our harrowing efforts along the bluff proved fruitful: a bounty of seeds await our preparation and shipment back to the US.