| Abstract: | The fossil history of the Fagaceae from China and its systematic and biogeographic
implications are discussed based on revisionary studies of the fossil records. No creditable
macrofossil record of the Fagaceae exists in the Cretaceous deposits and all the Cretaceous microfossil reports remain equivocal and require further study. The Paleocene fossils show the
appearance and diversification of the two groups corresponding to the subfamilies Fagoideae
and Castaneoideae sensu Nixon. By the Eocene, all modern genera had been present. The
oldest fagaceous fossils represent subfamily Fagoideae with affinities to the extant genus
Trigonobalanus. The leaf fossil genus Berryophyllum, with affinities to Quercus subg. Cyclobalanopsis, has been documented by the early Eocene and might have occurred earlier than
other fossils assignable to Quercus. The appearance of evergreen sclerophyllous Ouercus
with entire leaves might have occurred earlier than those with toothed leaves. Deciduous, urticoid-leaved oak fossils (Quercus subg. Quercus sect. Quercus) had not appeared until the
Miocene. Fossil equivalents of Trigonobalanus, Castanopsis and Lithocarpus had occurred
in Europe and North America by the early Tertiary, suggesting that continuous distributions
were achieved via the northern hemisphere land bridges. Three groups of evergreen sclerophyllous oaks of apparent close phylogenetic relationships occurred in the Hengduan mountains, the Mediterranean area and northwestern North America. Their fossil forms have become dominant elements of those vegetation zones since the Miocene. A shared fossil history
indicates a possible biogeographic boundary formed by the ancient Mediterranean. The evidence suggests that the oaks might arrive in North America during two distinct geologic periods: evergreen sclerophyllous entire-leaved oaks appeared by the Early Tertiary, whereas thedeciduous oaks with urticoid leaves appeared in the Late Tertiary. |
