Phylogeny of Fagus L. (Fagaceae) based on morphological data

Phylogenetic analysis of all modern and two fossil species of Fagus based on morphological characters strongly supports the subgenus Engleriana as a monophyletic group. This is based on several apomorphic features of vegetative structures, as cupule/nut and pollen characteristics in the three species constituting the subgenus Engleriana. Species of the subgenus Fagus form a paraphyletic grade basal to the subgenus Engleriana and display weak cladistic structure. This is mainly due to a high amount of morphological parallelism and essentially few phylogenetically informative characters among species of the subgenus Fagus. The North American F. grandifolia is most distinct among the species of the subgenus Fagus and shares some characteristics with the subgenus Engleriana. For Fagus weak differentiation is suggested during its early phase of dispersal in the Oligocene, accounting for the low resolution among its fossil and modern members. This is in agreement with at least one of three previous molecular studies on Fagus.