Betula globispica Shirai

Seldom seen in cultivation, Betula globispica is a rare species from the mountains of central Japan (Ohwi 1965; Oldfield, Lusty & MacKinven 1998). It forms a small, spreading tree with glossy leaves with quite deeply impressed veins. The golden yellow autumnal foliage and conspicuous fruiting catkins are both very ornamental; the latter remain on the tree for over a year.

Vegetative shoots of Betula globispica are superficially similar to those of B. ermanii, differing in the broader leaves with deeper and coarser teeth. However, the fruiting catkins are so distinctive that they could not be mistaken for those of any other birch except perhaps B. fargesii, being more or less spherical, with conspicuous spreading bract lobes when dry; the nutlets have no wing, merely a thickened rim. The fruiting catkins do not disintegrate readily and are so persistent that those from at least two successive years are usually present on the branches at the same time; attempts to detach the scales often end with the scales breaking. An unusual feature of this species, also seen in the closely related Betula chinensis, is that only one seed is produced in the axil of each fruiting catkin scale.

Two different accessions under this name were in cultivation at Darmstadt Botanic Garden by 1906, one of doubtful identity, another more recently acquired. The newer of the two was distributed to other institutions, including Sprenger’s nursery at Vomero – where it proved one of the only birches capable of thriving in the Neapolitan heat – and to Kew (Purpus 1906, 1907a, 1907b; Royal Botanic Gardens, Kew 1909). The material offered by Daisy Hill Nurseries, Newry, Northern Ireland seems likely to have originated from the same source (B[esant] 1919). A tree at Kew planted in 1957 (Bean 1970), obtained from Berlin Dahlem Botanic Gardens, is thought by McAllister and Ashburner (2013) more likely to have been B. fargesii. In modern cultivation, most if not all examples of the species derive from the 1981 introduction by Ness Botanic Garden, which obtained seed through H. Ohba, collected in Honshu near San’no, Kuriyama-mura, Tochigi Prefecture, by Rindo Kinenhi.

Experience at Ness Botanic Garden, England, suggests that Betula globispica is very sensitive to drought, even as a relatively well-established young tree. Five out of six seedlings established on light sandy soil at Ness later died of drought, even two that had already made good trees to 2 m with several main stems. The surviving tree is on heavy clay which, although wet, does not become waterlogged. While the tree does not seem to be fussy with respect to soil texture, a site should be chosen where the soil will never dry out; plants may even be tolerant of some degree of winter waterlogging. Betula globispica can be propagated easily by seed, although seedlings are slow-growing and highly susceptible to slugs and drought. The species is self-compatible: the trees raised at Ness first fruited when ten years old, producing large quantities of viable seed every year. Seed stored in a refrigerator for 12 years still shows excellent germination.