Article: Past global floristic changes: the Permian Great Eurasian Floral Interchange
It is widely held that during the Permian, especially the Late Permian, the Subangara flora spread southwards into China, where it mingled with the 'Cathaysian flora'. However, the reputedly Angaran or Subangaran elements found in North China, which are common in, or even characteristic of the Psygmophyllum Zone of that region, include gymnosperms such as callipterids, peltasperms and psygmophylloids, which are in fact Euramerican in origin. The evidence rather suggests that many Eurasian gymnosperms moved into Angara in the Late Permian, and were part of a large scale biotic exchange that may be termed the Great Eurasian Floral Interchange. It can be recognized as having occurred from two directions: from western Europe, via the Russian Platform into Angaran Pechora; and from the northern border of South China, via North China into Angaran Mongolia and eventually to the Kuznetsk. There was also some migration of Angaran elements into the neighbouring areas, but to a much lesser extent, and the floral interchange was thus clearly asymmetrical. The functional mechanisms driving the interchange were palaeomonsoons in the northern Palaeotethys, and the expansion of the Eurasian Arid Province.