These therefore rather reflect different ecological conditions than that they indicate different ages. The biostratigraphical value of these fossils is thus very limited. Another major problem is the facies development in the individual basins. The individual, mostly rather small intramontane basins, especially the Rotliegend basins, are often very difficult to correlate with each other. In some cases such correlations are also strongly hampered by the presence of considerable hiatuses.
Stephanian floras are much more common and therefore much better known than Rotliegend floras.
Especially in younger deposits plant fossils become rare. Although we know a relatively large number of plant localities from the Lower Rotliegend, there are only very few localities known from the Upper Rotliegend. Floras which are most probably coeval can be developed very differently. In these cases palynology, the study of fossil spores and pollen does not help any further, as palynomorphs are usually absent or very poorly preserved in redbed sequences. . During the Stephanian the conifers , a group of gymnosperms whose earliest representatives looked very similar to modern araucarians, became gradually more common.