EVOLUTIONARY TRENDS IN THE GENUS GINKGO

Abstract

Three main independent phylogenetic groups within Ginkgoales, consisting of different families, are suggested. It is considered impossible to deduce the genus Ginkgo from any other genus by means of fossil evidence known at present. The oldest finds of Ginkgo date from the Lower Jurassic. During the Cretaceous, increasing polymorphy in foliar remains indicates the rise of new species. During the Lower Cretaceous there also appears a type of leaf known both as G. adiantoides and as G. paradiantoides. This leaf is from the gross morphological and the anatomical point of view almost identical with the Tertiary and Recent Ginkgo populations, thus making a direct ancestry between the present-day Ginkgo and those of the Lower Cretaceous likely. By Lower Tertiary times a considerable reduction has taken place leaving only one gross morphological type of leaf, that of G. adiantoides. This is suggested to be identical with G. biloba. Although there is no positive evidence, it can be assumed that the final reduction of the genus, to its present-day East Asiatic home, has taken place during the Pleistocene period.