Abstract: The “lower” Hamamelidae sensu Endress (1989a) comprises seven fami- lies: Trochodendraceae,  Tetracentraceae,  Cercidiphyllaceae,  Myrothamnaceae, Eupteleaceae, Platanaceae and Hamamelidaceae. In the present paper, the systema- tic position, modern distribution pattern and fossil history of each family are ana- lyzed, and the origin and dispersal of them are discussed according to the princi- ple of the unity between the phylogeny and distribution of plants. The paper con- sists of three parts. The conclusions are as follows: 1. The center of distribution    According to Takhtajan's (1986) regionalization of the world flora, there are 13 distribution types in the “lower” Hamamelidae (Table 1 ). Eastern Asiatic Re- gion, with five families, 19 genera and 73 species, ranks the first based on the numbers of species,  genera and families. Four families:  Trochodendraceae, Tetracentraceae, Cercidiphyllaceae and Eupteleaceae which were considered as more primitive  in the  “lower” Hamamelidae  and three  genera: Disanthus, Exbucklandia and Rhodoleia, primitive in the Hamamelidaceae, are all found in Eastern Asiatic Region. In addition, the groups at different evolutionary stages in the “lower” Hamamelidae survive in this region. Indochinese Region, with two families, 15 genera and 32 species, ranks the second. It was shown that southern Eastern Asiatic region and northern Indochinese Region are the distribution center of the “lower”Hamamelidae based on further analysis (see Table 2).   2. The place and time of the origin   The fossil records of the “lower” Hamamelidae are abundant in angiosperms. Nordenskioldia, supposed as the extinct ancestral group of Trochodendraceae and Tetracentraceae, was widely distributed during the latest Cretaceous and the early Tertiary in the Northern Hemisphere; Trochodendroides  appeared during the Cretaceous in North America, former USSR and Japan;  the ancestral group of Cercidiphyllaceae,  the  Joffrea-Nyssidum  complex,  also  occurred  during  the Cretaceous in the middle and higher latitude area of the Norhern Hemisphere. In addition,  the  earliest  fossil  records  of the  Eupteleaceae,  Platanaceae  and Hamamelidaceae appeared in North America, Europe and Asia of the Northern Hemisphere  respectively.  Therefore,  the  Laurasian  origin  of  the “lower” Hamamelidae is supported by fossil evidence. On the other hand, the fossil data are still insufficient to determine the place of the origin, especially because the fos- sil records are rather poor in Asia. For this reason, the analyses of birthplace should combine with the information from the distribution of the primitive groups or outgroup of the “lower” Hamamelidae. Based on the statistics of distribution types, there are four primitive families in the “lower” Hamamelidae and three primitive genera in the Hamamelidaceae in southern Eastern Asiatic Region and northern  Indochinese  Region.  Platanus kerrii Gagnep. of the Platanaceae, distributed in northern Vietnam, is considered as one of the most primitive species which has survived in modern times in this family  because  of its  pistillate inflorescence  comprising  10-12  heads.  The Magnoliaceae was selected as an outgroup in our other paper “A phylogenetic analysis of families in the Hamamelidae” (Lu et al. 1991 ). All its 13 genera and most species occur from East to Southeast Asia, but in North America only three genera  are found.  Takhtajan (1969)  considered that  it  was  plants  of the Magnoliaceae that were dispersed from East Asia to North America. Because the primitive groups of the “lower” Hamamelidae and its outgroup almost occur in the same area, their ancestor also appeared most probably in this area according to the principle of common origin. It was inferred that the area from southern Eastern Asiatic Region to northern Indochinese  Region is the birthplace of the “lower"” Hamamelidae. The differentiation of the “lower” Hamamelidae took place rather early in angiosperms. The origin of them may be traced at least back to the Barremian of the early Cretaceous according to pollen fossil records. From more unequivocal fos- sil evidence,  Platanoid plants appeared during the late Albian of the early Cretaceous, and the Trochodendraceae,  Tetracentraceae,  Cercidiphyllaceae and Hamamelidaceae diverged from their ancestral groups respectively no later than the late Cretaceous (Fig. 6). 3. The causes for the formation of the modern distribution pattern The “lower” Hamamelidae is a. rather old group.  It is one of the most abundant and widespread components of fossil floras in the Northern Hemisphere during the late Cretaceous-middle Tertiary, the interval, when the global tempera- ture  was  warm,  although  the  extant  Trochodendraceae,  Tetracentraceae, Cercidiphyllaceae and Eupteleaceae which are now confined to East Asia are monotypical or oligotypical families. This distribution pattern indicates that most plants became extinct in Europe, northern Asia and North America because of the climatic changes during the late Tertiary, and especially the Quaternary glaciation, but East Asia, usually called “plant refuge”during the glacial period, became the survival place of many plants. From the viewpoint of evolution, these four fami- lies might be “living fossil plants” preserved from the Tertiary.   The distribution of Hamamelidaceae is disjunct, but the causes leading to this pattern are not the same in different genera.  The disjunction among Europe, North America, Australia and southern Africa is due to the tectonic movements of the earth; , and  that  between  southeastern  Europe-no