A MORPHOLOGICAL STUDY OF LIVING AND FOSSIL QUERCUS (OAK) POLLEN FROM CALIFORNIA USING LIGHT MICROSCOPY AND SCANNING ELECTRON MICROSCOPY

The pollen of Quercus (oak) is not usually classified below the genus level in palynological investigations of ancient vegetation, and this limits the amount of paleoecological information that can be extracted from the fossil pollen record. However, previous morphological work on Quercus pollen has shown that scanning electron microscopy (SEM) reveals details of ornamentation on the pollen surface that are too small to be imaged accurately using a transmitted light microscope, and can be used to group specimens of Quercus pollen into morphotaxa below the genus level. In this study, we have used the SEM to image the pollen of 23 species of Quercus that are native to California, and have grouped these into four morphotaxa on the basis of their surface ornamentation. Our results are comparable to previously published morphological investigations of Quercus pollen, and increase the number of taxa that have been studied in this fashion. We have also used the SEM to image fossil Quercus pollen in four sediment samples from Clear Lake, California. These samples are rich in Quercus pollen and date from the previous interglacial. Using our study of extant Californian Quercus pollen as a guide, we have grouped these specimens of fossil Quercus pollen from Clear Lake into three of the extant morphotaxa. Finally, we discuss the paleoecological significance of our results.