Abstract:

 The present paper aims to discuss the geog raphical distribution of the Juglandaceae

on the basis of unity of the phylogeny and the process of dispersal in the plants.

      The paper is divided into the following three parts:

      1.  The systematic positions and the distribution patterns of nine living genera in

the family Juglandaceae (namely, Engelhardia, Oreomunnea, Alfaroa, Pterocarya, Cyclo-

carya, Juglans, Carya, Annamocarya and Platycarya) are briefly discussed.  The evolu-

tional relationships between the different genera of the Juglandaceae are elucidated. The

fossil distribution and the geological date of the plant groups are reviewed.  Through

the analysis for the geographical distribution of the Juglandaceous genera, the distribu-

tion patterns may be divided as follows:

      A.  The tropical distribution pattern

      a. The genera of tropical Asia distribution: Engelhardia, Annamocarya.

      b. The genera of tropical Central America distribution: Oreomunnea, Alfaroa.

      B.  The temperate distribution pattern

      c. The genus of disjunct distribution between Western Asia and Eastern Asia:

Pterocarya.

      d. The genus of disjunct distribution between Eurasia and America: Juglans.

     e. The genus of disjunct distribution between Eastern Asia and North America:

Carya.

     f. The genera whose distribution is confined to Eastern Asia: Cyclocarya, Platy-

carya.

     2.  The distribution of species

     According to Takhtajan’s view point of phytochoria, the number of species in every

region are counted.  It has shown clearily that the Eastern Asian Region and the Coti-

nental South-east Asian Region are most abundant in number of genera and species. Of

the 71 living species, 53 are regional endemic elements, namely 74.6% of the total species.

The author is of the opinion that most endemic species in Eurasia are of old endemic

nature and in America of new endimic nature.  There are now 7 genera and 28 species

in China, whose south-western and central parts are most abundant in species, with Pro-

vince Yunnan being richest in genera and species.

     3.  Discussions of the distribution patterns of the Juglandaceae

A.       The centre of floristic region

B.         The centre of floristic regions is determined by the following two principles:  a.

A large number of species concentrate in a district, namely the centre of the majority;

b.  Species of a district can reflect the main stages of the systematic evolution of the

Juglandaceae, namely the centre of diversity.  It has shown clearly that the southern

part of Eastern Asian region and the northern part of Continental South-east Asian

Region (i.c. Southern China and Northern Indo-China) are the main distribution centre

of the Juglandaceae, while the southern part of Sonora Region and Caribbean Region

 (i.c. South-western U.S.A., Mexico and Central America) are the secondary distribution

centre.

      As far as fossil records goes, it has shown that in Tertiary period the Juglanda-

ceae were widely distributed in northern Eurasia and North America, growing not only

in Europe and the Caucasus but also as far as in Greenland and Alaska.  It may be

considered that the Juglandaceae might be originated from Laurasia.  According to

the analysis of distribution pattern for living primitive genus, for example, Engelhar-

dia, South-western China and Northern Indo-China may be the birthplace of the most

primitive Juglandaceous plants.  It also can be seen that the primitive genera and the

primitive sections of every genus in the Juglandaceae have mostly distributed in the

tropics or subtropics. At the same time, according to the analysis of morphological cha-

racters, such as naked buds in the primitive taxa of this family, it is considered that

this character has relationship with the living conditions of their ancestors.  All the

evidence seems to show that the Juglandaceae are of forest origin in the tropical moun-

tains having seasonal drying period.

      B.  The time of the origin

      The geological times of fossil records are analyzed. It is concluded that the origin

of the Juglandaceae dates back at least as early as the Cretaceous period.

      C.  The routes of despersal

      After the emergence of the Juglandaceous plant on earth, it had first developed and

dispersed in Southern China and Indo-China.  Under conditions of the stable tempera-

ture and humidity in North Hemisphere during the period of its origin and development,

the Juglandaceous plants had rapidly developed and distributed in Eurasia and dis-

persed to North America by two routes: Europe-Greenland-North  America  route  and

Asia-Bering Land-bridge-North America route.  From Central America it later reached

South America.

     D.  The formaation of the modern distribution pattern and reasons for this forma-

tion.

     According to the fossil records, the formation of two disjunct areas was not due to

the origin of synchronous development, nor to the parallel evolution in the two con-

tinents of Eurasia and America, nor can it be interpreted as due to result of transmis-

sive function.  The modern distribution pattern has developed as a result of the tectonic

movement and of the climatic change after the Tertiary period.  Because of the con-

tinental drift, the Eurasian Continent was separated from the North American Conti-

nent, it had formed a disjunction between Eurasia and North America. Especially, under

the glaciation during the Late Tertiary and Quaternary Periods, the continents in Eu-

rasia and North America were covered by ice sheet with the exception of “plant refuges”, most plants in the area were destroyed, but the southern part of Eastern Asia

remained practically intact and most of the plants including the Juglandaceae were

preserved from destruction by ice and thence became a main centre of survival in the

North Hemisphere, likewise, there is another centre of survival in the same latitude in

North America and Central America.

     E.  Finally, the probable evolutionary relationships of the genera of the Juglanda-

ceae is presented by the dendrogram in the text.