About 250 million years ago, four major floral provinces existed on the Earth's surface, the Gondwana Floral Province in temperate Southern Hemisphere, the Angara Floral Province in temperate Northern Hemisphere, and the Euroamerican and the Cathaysian floral provinces in tropical equatorial regions. These floras evolved as the continents drifted. The Cathaysian Flora is mainly distributed in most areas of today's China, Japan, and Southeast Asia. North China lies at the center of the origin of the Cathaysian Flora. During the Permian, the southern part of the North China Platform was located along the north shore of the northeastern arm of the Paleo-Tethys Ocean while at the same time the South China Platform was located its southern shore. The Yuzhou area of western Henan Province was located in the southern part of the North China Platform (western part of the Western Henan - Huaibei Gulf of the Paleo-Tethys Ocean). For a long time, this area was located in low-latitude epicontinental environments in a warm and humid climate. This unique paleogeographic position resulted in the transitional features of the sedimentology and biota between the North and South China platforms, famous for its coal-bearing strata that have "Northern Type with Southern Facies." Subsequently, a complete evolutionary sequence with abundant well-preserved plant fossils developed. The Permian outcrops in this area yield complete and successive sediments with abundant animal and plant fossils. In particular, plant fossils are exquisitely preserved and many taxa are endemic to the middle and late stages of the Cathaysian Flora, referred to as the Yuzhou Flora in this report.
The authors provide a comprehensive review on many aspects of the Yuzhou Flora, including its botanical features, evolutionary sequences and stages, plant assemblage zones, stratigraphic divisions and correlations, and plant ecological communities. The authors recognize 111 genera and 307 species from 40 fossil plant layers, including 25 new genera and 137 new species. The evolutionary sequences of some important groups, especially Gigantopteridales, are discussed. Based on studies of the abundant fossil material, the authors propose hypotheses related to the evolutionary trends in the leaf structure and leaf venation patterns and a new morphotype classification scheme for the Gigantopteridales. Also, the authors report the highest fossil horizon of the Cathaysian Flora of the North China Platform, which is primarily composed of the Gigantopteridales, advanced seed ferns (Peltaspermales), Ginkgoales, and Cycadales. Using Scanning Electron Microscopy (SEM), the authors investigated the in situ reproductive material of some anthrophytes and pteridophytes, and the results provide information on their taxonomic positions. The age of the major plant groups and their developmental stages are also discussed. Five plant assemblage zones, which correspond to the five lithostratigraphic units, are proposed. The development of the Yuzhou Flora is divided into three stages based on the changes of the paleoenvironments and paleoclimate, and the succession of the plants.,. Based on the development of major plant groups, the authors applied the principles of multiple stratigraphic division, including biostratigraphy, lithostratigraphy, and magnetostratigraphy, to propose a new division scheme for the Permian system on the southern part of the North China Platform, and to correlate them with coeval strata from adjacent areas. This will provide basic information related to the study of the stratigraphic stages of Permian system from the North China Platform.
The team, led by the senior author, Professor Yang Guanxiu, started studying the Yuzhou Flora in 1979. The team has collaborated with the Coalfield Geology Department at the China University of Geosciences (Beijing), the Geological Survey of Henan Province, and the Pingdingshan Coal Field. Two projects sponsored by the National Natural Science Foundation of China have been successfully completed. The projects have produced many research publications, including the monograph The Permian Cathaysian Flora from western Henan, China: the Yuzhou Flora, and have provided many training opportunities for graduate students. This achievement represents the first in-depth scientific research on the Cathaysian Flora since T. G. Halle (1927) and Li Xingxue (1963).