Shrub 2–4 m tall, usually monoecious, rarely dioecious. Branchlets spreading, tinged purple and pubescent when young, later glabrescent. Leaves ovate, simple or 3-lobed, 3–7 × 3–4.5 cm, subglabrous beneath, rough to touch above, margin triangular serrate, apex attenuate to short-acumindate; petiole c. 1 cm, pubescent at first, later glabrescent. Male inflorescences globose, 0.8–1 cm across. Female inflorescences globose, pubescent. Male flowers: calyx 3- or 4-lobed, lobes triangular, pubescent beneath, anthers elliptic. Female flowers: calyx tubular, apically toothed, lobed, or entire, style 1, papillate at middle. Syncarp 0.8–1 cm across, with stellate clusters of firm, barbed hairs. (Cullen et al. 2011; Wu, Zhou & Gilbert 2003).
Distribution Japan North Korea (?) South Korea
RHS Hardiness Rating H3
Long considered a species in its own right in horticultural literature, recent research confirms Broussonetia × kazinoki is actually a hybrid of B. papyrifera and B. monoica (Chung et al. 2017). Western horticulture’s apparent reticence to recognise it as a hybrid is, perhaps, explained by the fact only this taxon and B. papyrifera are grown in our area, but within its native range and especially in Japan it has long been cultivated for the production of high-quality paper. Indeed, it seems to be the favoured taxon for this purpose in Japan, where it is known as Kōzo.
It was probably introduced to Europe in the 19th century, but here it has always played second fiddle to the larger, showier, and more versatile B. papyrifera. In contrast with that arborescent species B. × kazinoki is consistently shrubby in western gardens, forming a wide-spreading, lax shrub of rather open habit. Chung et al. (2017) emphasise its ‘highly variable’ nature, with plants occupying a spectrum of character states between the two parents, but these observations are based on populations within its natural range where it has been cultivated for over a thousand years, and the population cultivated in western gardens is, by comparison, rather uniform. In these areas it can be distinguished from B. papyrifera by the shorter male inflorescence, shorter petioles, and by the sparsely pubescent and later glabrous young shoots and leaves (Bean 1976). Its second parent, B. monoica, is not known to be cultivated in our area. Bean noted that B. × kazinoki was once cultivated under the erronous name B. kaempferi, but the true B. kaempferi is a woody liana native to warm-temperate to sub-tropical areas of mainland south east Asia and southern Japan (Chung et al. 2017; Bean 1976).
Reportedly raised by Barry Yinger and distributed in the early 2000s by his Asiatica Nursery, Pennsylvania, USA, ‘Color Palette’ is described as having leaves ‘mottled cream, yellow, and green’ (Hatch 2021-2022).