PHYLOGENY OF THE CHAROPHYTA

Abstract

Summary The affinities of the phylum Charophyta and the general evolutionary trends undergone by this group since the Late Silurian are discussed briefly. The main emphasis is placed on the Mesozoic family Clavatoraceae as the rapid changes in the utricle, a supplementary envelope investing the female gametangium, have led to quite diversified and elaborate structures that allow more detailed phylogenetic studies. Three lineages are analysed which, throughout the Lower Cretaceous, show a sequence of gradual changes linking quite distinct extreme types. These lineages concern respectively the genus Globator , the genera Perimneste and Atopochara , and the genera Flabellochara and Clypeator , for each of which new data are presented. The relationships between the three subfamilies and the several genera of the Clavatoraceae are discussed, as well as the mode of extinction of the group at the end of the Cretaceous and the rates of taxonomic evolution in the studied lineages. A biochronological zonation is established for the Lower Cretaceous on the basis of the three described evolutionary sequences. The zonation, with nine biozones from the Berriasian to the Cenomanian, seems to be useful in correlating non‐marine formations on a worldwide scale.