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A monotypic genus native to southeast China.
A potentially large deciduous, monoecious tree. Branchlets with chambered pith. Leaves imparipinnate. Inflorescences pendulous catkins: male in clusters of 3–5, lateral on old growth; female solitary, terminal on new growth. Fruit a disc-winged nutlet with 2 or 4 chambers (Lu et al.1999.)
The extraordinary disc-winged fruit of the Wheel Wingnut are conspicuous and attractive. Introduced as early as 1901, this rare tree had a 'false start' in cultivation, and only after a much more recent introduction is it beginning to make its presence felt in specialst collections.
The closest relatives of Cyclocarya are the wingnuts (Pterocarya), the walnuts (Juglans), the hickories and pecans (Carya), and a single species of Platycarya (Manos et al. 2007; Mostajeran et al. 2017).These phylogenetic studies, whilst not complete, suggest that Cyclocarya is sister to either Pterocarya or Juglans plus Pterocarya, and that it does not nest within either of those genera. Cyclocarya and Pterocarya together are easily distinguished from Juglans and Carya by their much smaller, winged nuts on hanging catkins, and from Carya by their chambered pith. Platycarya differs again as it has much smaller, narrow-winged nuts, a solid pith and a strikingly erect male catkins and infructescences. Cyclocarya is distinguished from Pterocarya by the shape of the nut wing. Pterocarya has a pair of wings, whilst in Cyclocarya the wing forms a leathery disc right round the fruit. Pterocarya wings represent a pair of bracteoles, whilst in Cyclocarya the ring results from fusion of these bracteoles plus (to a variable extent) a bract. The male catkins of Cyclocarya are borne in clusters of 3-5 (singly in Pterocarya). Cyclocarya has a base chromosome number n=28, as opposed to n=16 in Pterocarya (Manos & Stone 2001; Crane & DuVal 2013; Kozlowski et al. 2018).
Fossil Cyclocarya fruits first appeared in the late Paleocene of North America, around 55 million years ago (Manchester 1987). There was a great radiation of fruit forms in the Juglandaceae around this time, not all of which survive in living species. The genus spread across Europe to Asia, becoming extinct in North America rather quickly, but persisting in Europe until the Ice Ages of the Pleistocene restricted its range to East Asia (Manchester et al. 2009; Crane & DuVal 2013).
The one living species, Cyclocarya paliurus, was originally published as Pterocarya paliurus. It was segregated as a separate genus in 1953 by the Russian botanist Irina Iljinskaya; despite opposition from Manning (1978) it is generally accepted today, for example by Flora of China (Lu et al. 1999). The generic name refers to the wing (Greek kyklos, a circle and karyon, a nut).