PLEUROMEIA-STERNBERGII (MUNSTER) CORDA FROM THE LOWER TRIASSIC OF GERMANY - FURTHER OBSERVATIONS AND COMPARATIVE MORPHOLOGY OF ITS ROOTING ORGAN

Three rather well preserved rhizophores of Pleuromeia sternbergii from the type-locality Bernburg (Saale, Germany), as well as Magdefrau's specimen have been re-examined. They provide new data which serve as a basis for reconsidering their structure. A lectotype was chosen from the original material. For the first time a very small rhizophore, probably immature, is described and figured. The characteristic features, e.g. rhizophore anatomy, number of lobes, root structure, arrangement, sequence of initiation and course of traces are analyzed and discussed. Careful consideration of root-scar arrangement, furrow structure and root-trace course yields the first structural evidence demonstrating the organization of the vascular system, the process of root production, the weak cortex development and the long root retention in P. sternbergii. Comparison is made with the living genus Isoetes and other lobed and furrowed lycopods. Their place in the evolutionary history of the lycopods, particularly with regard to the cormose lycopods and those with stigmarian branching, is reviewed.