PHYTOGEOGRAPHIC DIFFERENTIATION DURING THE LATE VISÉAN WARM PHASE BEFORE THE ONSET OF THE LATE CARBONIFEROUS ICE AGE

The late Viséan experienced the warmest conditions of the Early Carboniferous just before the onset of icehouse times. Phytogeographically the late Viséan showed a differentiation not only into the major realms but also subdivisions within them. In the Euramerian Realm we can distinguish now a particular province that included Alaska, the Canadian Arctic, Greenland, and Svalbard (Spitsbergen). Floras from these areas consist of arborescent lycopsids and pteridosperms that grew in fluvial environments and on the margins of lakes. Their limited diversity distinguishes them from other tropical floras in the realm.

There has been some debate if a Cathaysian Realm can be distinguished in the tropics of this interval or if one should rather use the term Amerosinian Realm for the entire tropical vegetation. Many common taxa are identical but the Cathaysian area is characterized by many endemic species and genera. It was also the area where significant taxa such as the paripterid pteridosperms originated and subsequently spread to other tropical areas. Both factors seem to justify a separation as a realm.

In the Gondwana Realm, a particular warm temperate flora was widespread that has been described as the Paraca floral belt. These floras are composed of endemic forms and immigrants from either the tropics or the northern temperate Angara Realm. These floras are clearly distinct from those the cooler climate closer to the South Pole.

Different quantitative methods clearly show the degree of difference and similarity reflecting well developed zonal (biome) and phytogeographic differentiation in the late Viséan.