作 者 ：Li Jian-qiang
期 刊 ：植物分类学报 1996年 4期
Keywords:Fagaceae, Distribution,
Abstract:On the basis of unity of the phylogeny and the process of dispersal in plants,the origin and distribution of the fagaceous plants are discussed. For some important problems about the systematics of Fagaceae,the author proposes his point of views. The main conclusions are as follows:The distribution pattern of genera:The living genera of Fagaceae are divided into four disjunct distribution patterns, i.e., 1. The genus of disjunct distribution between tropical Asia and tropical Central America: Trigonobalanus. 2. The genera of disjunct distribution between Asia and west of North America: Lithocarpus, Castanopsis 3. The genera of disjunct distribution between Eurasia and North America: Castanea, Fagus 4. The genus of disjunct distribution between Eurasia, North Africa and America: Quercus.The distribution of species: Based on Takhtajans opinion of phytochoria, about 880 living species of six genera in this family occur in 11 regions of three kingdoms. Among them, both genera and species are most abundant in the East Asian Region(5 genera, 261 species) and the Southeast Asian Region (4 genera, 283 species). Of living species, 541 are regionally endemic elements( excluding endemic species of Quercus in America , see Table 1), namely 61% of the total. In America and Europe, endemic species are mostly of neoendemic nature because about 95% of them come from the advanced subgenus Quercus, however, those in Malaysia, Southeast Asian and East Asian Regions are of paleoendemic nature. There are six genera, 320 species,about 40 subspecies and varieties in China. Southwest and south China are most abundant in species and Yunnan province is the richest in both genera and species (6 genera, about 176 species). Distribution patterns of the Fagaceae: As known at present, there are two distribution centres of the floristic region. Southern East Asia to northern Sout heast Asia is determined as the main distribution centre, where occur not only the majority of genera and species, but also the primitive and advanced forms of genera and species; and southern Madrean to Carib bean region(Southwest U S A, Mexico, Central America) is the secondary distribution centre, where over half of the total species of the advanced genus Quercus are distributed, but of the other genera of Fagaceae,only one species is known occurring in Madrean and Caribbean Regions. The place of origin: In tropical and subtropical regions, the evergreen fagaceous plants have several flushes a year. Northern Fagaceae are usually presumed to have a single flush, but in Nebraska of the United States, five deciduous species of Quercus were also observed to have as many as five flushes during a wet summer. It could be assumed as atavism if it is found in the deciduous oaks and should be used as evidence that the fagaceous plants originated from the tropical region. And both the primitive and advanced genera of Fagaceae, including the primitive infrageneric taxa ( for example, Lithocarpus elegans, and the subgenus Cyclobalanopsis of Quercus) are mainly distributed in south and southwest China and north Indochina. Additionally, the living primitive genera of Hamamelidaceae which is usually considered phylogenetically closely related to Fagaceae are mainly distributed in above mentioned region. So it is quite possible that in the region the tropical mountains with a dry season is the birth place not only for Hamamelidaceae but also for Fagaceae.The time of origin :Nothofagaceae is recently treated as a sister group of Fagaceae. Its pollen, a kind of very distinct type( exine echinulate) occurred from the early Campanian of the upper Cretaceous, and the characteristic Castaneoid Tricolpoloenites Pollen are found from the Santonia and Santonia Campania. So the original time of Fagaceae can be probably determined at the early period of the upper Cretaceous.The routes of dispersal: The land bridges were very important to the distribution of fagaceous plants in upper Cretaceous and early Paleocene. When the climate and geographical conditions were very convenient, the fagaceous plants developed and distributed rapidly. From the original locality they entered America mainly by two routes: The plants of Trigonobalanus、Lithocarpus and Castanopsis were possibly distributed via EurasiaGreenlandbridges (including many nowsunken islands in Atlantic Ocean) to America. The Lithocarpus fossils found from the Paleocene of Europe and Eocene of the North America confirms the presence of this dispersal route. But the deciduous oaks in the North America came from the East Asia via Beringlandbridge. From North America, they extended to Central and South America.The formation of the modern distribution pattern and reasons for this formation might be concluded as follows. The modern distribution pattern of living fagaceous plants is due to the results of continental
drift,the glaciation effect, and biological characters of plants themselves.For example, the plants of Lithocarpus, Castanopsis and Trigonobalanus had been extensively distributed in Eurasia and America before the Pleiocene. The diminution and disappearance of their distribution region was mainly the results of the southward removal of the equatorial belt after the Oligocene and the glaciation effect in the Quaterary. The fossil evidence shows that the Lithocarpus plants disappeared during the period of Pleiocene in Europe. The delay of the life history cycle is also an important fact affecting the formation of the distribution region especially for the most plants of Lithocarpus and Castanopsis whose fruits mature in the autumn of the second year. Finally, based on the synthetic data, a discussion about the possible evolutionary relationships within the Fagaceae is presented.
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