| Author||C.G.G.J. van Steenis|
|Title||Nothofagus, key genus of plant geography, in time and space, living and fossil, ecology and phylogeny|
|Journal||Blumea - Biodiversity, Evolution and Biogeography of Plants|
|Abstract||Data are given on the taxonomy and ecology of the genus.|
Some New Caledonian species grow in or descend to the lowland. Details are provided on the distribution within New Guinea. For dominance of Nothofagus, and Fagaceae in general, it is suggested that possibly symbionts may contribute to this. Some notes are made on regeneration and germination in New Guinea.
A special chapter is devoted to a discussion of dispersal which appears to be extremely slow, with the implication that Nothofagus indubitably needs land for its spread, and has needed such for attaining its colossal range, encircling onwards of New Guinea the South Pacific (fossil pollen in Antarctica) to as far as southern South America. Map 1.
An other chapter is devoted to response of Nothofagus to the present climate. The possibility is envisaged that it could have grown along the border of the Antarctic Continent during a milder climate in the Cretaceous and Tertiary.
The fossil record is ample, both by macrofossils and fossil pollen. Of the three pollen types, the brassii and fusca types are already found in the Upper Cretaceous in Australia, New Zealand, and Antarctica, and in the Eocene in Fuegia the menziesii type being found hitherto not earlier than the Lower Tertiary. Table 1.
No reliable Nothofagus fossils have ever been found on the northern hemisphere. There it is represented by its counterpart, Fagus, with which it forms the subfamily Fagoideae of the family Fagaceae. Macrofossils of Fagus are known from the Tertiary and possibly also from the Upper Cretaceous (on the northern hemisphere to a fairly high latitude. Map 1.
Nothofagus is called a key genus for plant-geography because it meets the three criteria for safe biogeographical reasoning, viz. it has a sound taxonomy, an ample fossil record, and diaspores for which long distance dispersal is excluded.
Fagoideae occupy a remarkable hour-glass-shaped bi-hemispheric range, with the contraction in the Malesian tropics. Map 1. Whereas even at present the largest amount of morphological diversity of Fagaceae in the world is found in Malesia (Lithocarpus: various sections, Quercus, Castanopsis, Trigonobalanus, and Nothofagus), with Castanea and Fagus in the Sino-Himalaya, it is likely that the cradle of Fagoideae was somewhere in the region stretching from Yunnan to Queensland. It is reasonable to assume that from this initial pre-Upper Cretaceous Fagaceous matrix Fagus emerged in the northern part and Nothofagus in the southern part, for which Queensland looks the most likely.
It is shown that the evolution and spread of Nothofagus can be explained in an unforced way under the steady state principle, which implicates that certain oceanic areas in the South Pacific have been land in the Cretaceous or Early Tertiary.
This north-south bi-hemisphere pattern of distribution is found in many groups, sometimes in the rank of family, sometimes in the lower rank of genus or even in rare cases of species. Ranges may be almost intact in the tropical-montane zone, as happens to be in Euphrasia which possesses a range almost replicating that of Fagoideae. Map 2. In others the tropical transition relicts are very rare or even absent. The rare ones are sometimes taxonomically highly interesting by being systematically isolated and showing unusual characters.
It is advocated that the tropical montane representatives of this pattern of distribution have gained their range synchronously or almost so, as the series of opportunities enabling such ranges to develop is supposed to have happened only ‘once’ in geological time. This implies that taxa belonging to ‘morphologically advanced’ groups are of greater antiquity than formerly often supposed.
The main conclusions have been framed in a number of theses (Chapter 13).
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