CASTANEOID INFLORESCENCES FROM THE MIDDLE EOCENE OF TENNESSEE AND THE DIAGNOSTIC VALUE OF POLLEN (AT THE SUBFAMILY LEVEL) IN THE FAGACEAE

Abstract

In order to help evaluate the actual affinities of four types of inflorescences that shared gross pollen and inflorescence morphology with the extant Fagaceae, the pollen of the extant Fagaceae was analyzed with light, scanning, and in some cases transmission electron microscopy. The survey illustrates the range in pollen structure in the Fagaceae and confirms that exine ornamentation is a good diagnostic character for determining subfamilies within the modern Fagaceae. Careful comparison of the pollen and floral morphology of the fossils with similar features of the extant Fagaceae revealed only one of these fossil inflorescences was actually fagoid (the other inflorescences will be considered in a subsequent manuscript). The fagaceous inflorescences are catkins conforming in all aspects of pollen, inflorescence, and floret morphology with catkins of the modern subfamily Castaneoideae. The fossil catkins also share the relatively robust inflorescence axis with modern castaneoid inflorescences suggesting that they, too, may have been upright and insect pollinated. The nature of these fossils is consistent with observations that several other families of the “Amentiferae” evolved rapidly during the Upper Cretaceous‐Middle Eocene and this trend suggests that conditions favoring wind pollinated arborescent angiosperm species were optimal during that interval.