Wood Anatomy of Modern and Fossil Fagales in Relation to Phylogenetic Hypotheses, Familial Classification, and Patterns of Character Evolution

Abstract

The wood anatomy of fagalean families is summarized. Each family and most genera are wood anatomically distinct and can be distinguished by features such as vessel grouping and arrangement, vessel-ray parenchyma pit type, imperforate element type, ray structure, and axial parenchyma distribution. For each family, we review the published fossil wood record (with particular attention to Cretaceous and Paleogene occurrences) that we consider to be reliably identified on the basis of diagnostic character syndromes, giving insights into their stratigraphic range and former geographic ranges. Fossil woods with characteristics of the Fagaceae (Castaneoideae) occurred as early as the Late Cretaceous (Campanian) of the Northern Hemisphere and were widespread in the Cenozoic. Nothofagaceae wood occurred in the Late Cretaceous and Early Tertiary of Antarctica. Ring-porous Castaneoideae were not common until after the Eocene, reflecting the increase in seasonality that occurred in the Northern Hemisphere at that time. Woods diagnostic of Betulaceae, Juglandaceae, and Myricaceae occurred in the Eocene. With the recognition of Morella Lour. as a genus distinct from Myrica L., we propose two new combinations for fossil woods of Myricaceae. Reliably identified Casuarinaceae wood did not occur until the Miocene. There are no reports of Ticodendraceae fossil wood, although there are reports of fossil woods with its combination of features from the Cretaceous onward, but these are assigned to different families or are of unknown affinities. Most fagalean fossil woods have anatomy similar to that of modern genera, but some Paleogene taxa have combinations of characters not found in present-day genera. We discuss the utility of wood anatomy in assessing phylogenetic relationships within and among families of Fagales, with reference to clades supported by molecular sequence data. Generally, wood anatomical groupings are consistent with recent phylogenetic analyses of the order and of its constituent families. We propose hypotheses about adaptive character evolution in the order based on previously presented phylogenetic relationships inferred from DNA sequence data and the current ecological preferences of individual families.