In this paper the author discusses the rise of the four paleobotanical provinces in the latest Paleozoic era and the cause of their disappearance in the latter part of the Triassic period.
It was the late Silurian period that the vascular plants advanced onto the land for the first time. Through the Devonian period these plants attained remarkable evolution and laid the foundation for the great development of plants in the Carboniferous period.Since the late Silurian period up to the time of the early Carboniferous
Lepidodendropsis flora, the plants had a strong uniformity, with same genera or same species widely distributed from Spitsbergen in the north to the southernmost tip of South Africa. With the appearance of glaciers in the late Carboniferous period, the plants began to show some regional characters, and during the Permian period four distinct floral provinces, in the east, west, north and south, come into existence. The Euramerian province in the west of the equatorial zone was represented by the Euramerian flora which continued from the Carboniferous plants. In the east there was the Cathaysia province represented by the
Gigantopteris flora consisting mainly of
Gigantopteris nicotianaefolia, Bicoemplectopteris hallei and
Lobatannularia heianensis. In the Gondwana province of the Southern Hemisphere, the
Glossopteria flora (Gondwana flora) consisting chiefly of Glossopteridales made its appearance, while in the Northern Hemisphere there was the Angara province represented by the Angara flora characterized by such genera as
Angaropteridium, Angaridiunz, Paragondwanidium and
Glottophyllum.
The equatorial zone of those days can be located on the map by plotting the equator obtained from the paleomagnetic study (Fig. 3). It is inferred from the map that the Euramerian flora and the Cathaysia flora were distributed roughly along the equatorial zone, the Gondwana flora was distributed encircling the South Pole, and the Angara flora was in the vicinity of about lat. 30°-40°N.
According to the author's study, the simple leaf of
Gigantopteris and
Glossopteris was derived from the pinnate leaf either by fusion or enlargement of segments which took place when the plant growth was retarded by the severely changing environment. The fact that the Cathaysia flora had simple-leaf Gigantopteridales indicates that the harsh environment caused repeated fusion of leaf, eventually resulting in the formation of simple leaf, whereas the appearance of simple-leaf Glossopteridales in the Gondwana flora means that the much deteriorated environment caused enlargement repeatedly so as to form the simple leaf.
When the greater part of the Gondwana flora is occupied by simple-leaf plant, no simple leaf is found in the Angara flora. This seems to suggest that the environment of the Angara province in the north was milder than that of the Gondwanaland in the south.
Likewise, the Euramerian province in the west was apparently in a milder environment than the Cathaysia province in the east, because the simple-leaf Gigantopteridales are found in the Cathaysia flora while no simple leaf occurs in the Euramerian flora.
The severity of the environment of the Gondwanaland is attributed to low temperatures as evidenced by the appearance of glaciers, whereas in the Cathaysia province the environmental severity is due to the increasing annual range of climate and the aridness as the land gradually became a continent.
Thus, the results of the paleobotanical study and the paleomagnetic study seem to be in good accord.
It can be concluded, therefore, that the rise of the four different floral provinces toward the end of the Paleozoic era is ascribed to the upheaval of the land, on account of which the continental climate came to prevail, the glaciers formed in the Southern Hemisphere and the equatorial zone turned arid.
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