The biogeography of Nothofagus and Trigonobalanus and the origin of the Fagaceae

The suggestion that Trigonobalanus excelsa reached Colombia by migration from south-east Asia via the Bering land-bridge is criticized. The distribution of Trigonobalanus can be more simply explained by the disruption and drift of the former Pacific continent and the peninsula of West Gondwanaland. All but the New Guinea species of Nothofagus remain on the drifted fragments of the Gondwana peninsula, the original home of the family. Drift accounts for the present disjunct distribution of related Nothofagus species in the Southern hemisphere, but topoclines in characters of the fructifications and of the leaves linking New Zealand, New Caledonia and New Guinea indicate the overland migration route into the Pacific continent. Diversification of the family occurred in Pacifica before that continent was disrupted in the late Jurassic. With the formation of Eurasia, a topocline in leaf characters developed in Fagus along the migration route from China to Western Europe. Absence of topoclines involving the Bering land-bridge indicate that this bridge played no significant part in the dispersal of the Fagaceae. Shedding of the fruits of Glossopteris before the development of an embryo draws attention to the primitive character of delay in fertilization found in Nothofagus.