Acer shirasawanum 'JORDAN' Shirasawa maple, Japanese maple

Acer

Acer shirasawanum, the Shirasawa maple, is a species native to Japan, where it grows in the mountainous regions of central and southern Honshu and on the islands of Shikoku and Kyushu. It occurs there as an understorey tree or large shrub in cooler, humid forests, often on steep slopes with humus‑rich, well‑drained soils. Unlike Acer palmatum, which occupies a wide ecological range, A. shirasawanum is more typical of higher elevations and stable montane climates, a pattern reflected in its slower growth and marked tolerance of partial shade. It belongs to the same taxonomic group as A. palmatum, A. japonicum and A. sieboldianum, and differs from the first two mainly by its smooth, hairless shoots and upright inflorescences, while in contrast to the yellow‑flowered A. sieboldianum it bears red flowers. The leaves are almost circular, deeply lobed, with 9–13 shallow, finely serrated lobes that turn vivid shades of gold, orange and red in autumn. The species was described in 1911 by the Japanese botanist Gen’ichi Koidzumi and named in honour of Homi Shirasawa, who studied the dendroflora of Japan. In cultivation it is less common than Acer palmatum, but its cultivars rank among the most valuable Japanese maples, many of them having received international awards for ornamental merit. By 2020, seventeen recognised cultivars had been registered, each with its own distinctive qualities.

The Shirasawa maple is one of the species that remained hidden for centuries in Japan’s mountain forests and entered cultural awareness later than the widely cultivated palmatum maples. In Japanese it is known as Ōitaya meigetsu, the “moon leaf”, a name referring to its almost circular, finely divided foliage, which in traditional aesthetics evokes the clear autumn moon. In its native regions of central and southern Honshu, Shikoku and Kyushu it forms part of the autumn tradition of momijigari (紅葉狩り), the “hunt for red leaves”, when people travel to temple gardens, mountains and parks in search of the finest colours. It is a celebration held in similar esteem to the spring hanami (花見), dedicated to flowering cherries. Compared with the deep reds of A. palmatum, the golden and orange tones of this species create a lighter, calmer counterpoint. Japanese maples appear throughout literature — in the Man'yōshū, the oldest surviving anthology of Japanese poetry from the 8th century, and in Chinese poetry, where they were praised by writers such as Wang Wei (699–759). For centuries they have been a constant motif in painting, woodblock prints, textiles and porcelain, symbolising beauty, elegance, tranquillity and the transience of the seasons — qualities that have become part of the aesthetic code of the entire East Asian cultural sphere. Their leaves are used in ikebana and seasonal decorations, appear in the tea ceremony as an emblem of autumn, and in the Minoo area near Osaka they are prepared as the regional speciality momiji no tenpura (もみじの天ぷら), a sweet treat made from salted and batter‑fried maple leaves.

The modern era of Japanese maples is shaped by several key figures and institutions that define the direction of breeding and scholarly documentation. In the Western world, a pivotal role was played by the American dendrologist J. D. Vertrees (1920–1993), author of the first comprehensive monograph Japanese Maples, followed by the British specialist Peter Gregory, long‑time curator of the collection at Westonbirt Arboretum. In Europe, one of the most important centres is the Dutch arboretum and nursery Esveld, run by the van Gelderen family (est. 1865), while in Japan traditional nurseries such as Tsukasa Maple and Kobayashi Momiji‑en preserve old regional clones and introduce new cultivars. Among the world’s leading collections are Westonbirt Arboretum in the United Kingdom, the Arnold Arboretum of Harvard University (est. 1872), which has long studied the genus Acer, and the Portland Japanese Garden, where Japanese maples have become an iconic feature and the focus of expert care. In Japan, key institutions include the Kyoto Botanical Garden (est. 1924) and the Koishikawa Botanical Garden in Tokyo (est. 1684), both of which maintain the genetic diversity of native forms.