Cercidiphyllum is a genus of two species of large deciduous trees, both commonly known as katsura, and the sole members of the monotypic family Cercidiphyllaceae. The genus is placed in the order Saxifragales and is native to Japan and China. Despite a superficial resemblance in leaf shape, it is unrelated to Cercis (the redbuds).
The type species, Cercidiphyllum japonicum, is among the largest hardwoods in Asia, capable of reaching 45 m (148 ft) in the wild. The second species, C. magnificum, is considerably smaller, rarely exceeding 10 m (33 ft). Both species produce short spur shoots along their twigs bearing broadly heart-shaped, palmately veined leaves, while the long shoots carry elliptic to broadly ovate leaves — a dimorphic arrangement distinctive within the family. The genus is dioecious, with male and female flowers borne on separate trees. Flowers are small and inconspicuous, appearing in early spring before the leaves and are wind-pollinated. The fruit consists of clusters of 2–4 small pods, each 1–2 cm long, containing numerous small, flattened, winged seeds that are released from autumn through winter.
A celebrated characteristic of katsura is the sweet, caramel-like scent released by the browning leaves in autumn, caused by the compound maltol. In German-speaking countries the tree is nicknamed Kuchenbaum ("pie tree") or Lebkuchenbaum ("gingerbread tree") in recognition of this fragrance. The genus is cultivated widely as an ornamental for its delicate foliage, vivid autumn colour, and fast growth where adequate soil moisture is available.
Etymology
The name Cercidiphyllum means "Cercis-leaved," from the genus Cercis (redbuds) and the Greek phyllon (leaf), referring to the similarity in leaf shape between the two unrelated genera. Despite this resemblance, Cercidiphyllum and Cercis are not closely related.
Distribution
Cercidiphyllum is native to Japan and China. C. japonicum occurs throughout this range and was formerly divided into a Chinese variety (var. sinense), though no consistent morphological difference between Japanese and Chinese populations has been established. C. magnificum is endemic to central Honshū, Japan, where it grows at higher altitudes than C. japonicum.
Cultivation
Katsura is widely grown as an ornamental tree for its delicate heart-shaped leaves and vivid autumn colour — a mixture of bright yellow, pink, and orange-red. Where soil moisture is adequate it is fast-growing, but the genus is very sensitive to drought and requires deep, permanently moist soil; under dry conditions trees will shed leaves, though refoliation can occur once water is restored. Trees naturally sucker from the base when young and become multi-stemmed at maturity; pruning to a single stem is not recommended. Several weeping cultivars of C. japonicum are in cultivation, including the excurrent 'Morioka Weeping' (originating in Morioka City, Japan) and the rounded weeping clones 'Amazing Grace' and 'Tidal Wave'. Both C. japonicum and the weeping form C. japonicum f. pendulum hold the Royal Horticultural Society's Award of Garden Merit.
