Ancient Dasycladales and Charophyta: convergences and differences, with special attention to Munieria baconica

Abstract

We present a new morphological study of the Cretaceous species Munieria baconica, combined with a critical analysis of charophyte thalli, with the aim of determining the systematic attribution of the genus Munieria, either to the Dasycladales or to the Charophyta. Our study shows that thalli of M. baconica are organized as in the Dasycladales: they possess a central stem, on which arise whorls of primary branches (radial canals), each bearing at their distal end a cluster of secondary branches with calcified internal partitions resembling rose windows. There appears to have been cytoplasmic continuity between the different organs composing the thallus, as in Dasycladales. Charophyte thalli, however, are multicellular; the central canal never ramifies internally, and spine-cells forming structures like rose windows arise from cortical cells. The thalli of the clavatoracean charophyte Septorella ultima, which has been designated as a Munieria species by several authors, differ totally from those of Munieria. Emended diagnoses of the genus Munieria and of its type species M. baconica are given. From a palaeoecological point of view, the co-occurrence of M. baconica and Atopochara trivolvis (Clavatoraceae) in the type locality of M. baconica in the Bakony Mountains (Hungary) confirms that fossil dasyclads can inhabit brackish environments, as do, for example, recent Batophora species.