Journal of the Faculty of Science, Hokkaido University. Series 4, Geology and mineralogy;Vol.XIX, No.4


The Revision of the So-Called "Cercidiphyllum" Leaves from the Paleogene of North Japan

Tanai, Toshimasa

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Leaves superficially similar to Cercidiphyllum have been commonly reported from the Paleogene of the Northern Hemisphere. These leaves include various shapes with acrodromous veins, and with crenate to nearly entire margin. My recent investigation of the fine venation character reveals that Paleogene leaves referred once to Cercidiphyllum from Japan contain various genera such as Cocculus, Disanthus, Populus and Tetracentron. Leaves of Cocculus and Disanthus with no marginal glands are easily excluded from Cercidiphyllum-like fossils. On the other hand, leaves of three genera, Populus, Tetracentron and Cercidiphyllum, are liable to confuse each other. Populus leaves are usually small in areolation intruded by thick veinlets with asterate branching, while leaves of Cercidiphyllum and Tetracentron are mostly large in areolation intruded by thin, irregularly branching veinlets. There are, however, some marked differences in the secondary looping and venation within the teeth area between the typical leaves of Cercidiphyllum and Tetracentron, but their feutures contain many exceptions. The nature of marginal glands is a most note-worthy distinction between these two genera. The combination of the above-noted characters can lead to accurrate generic assignment of "Cercidiphyllum" leaves in the Paleogene.