Cryogenian glacial habitats as a plant terrestrialization cradle – the origin of Anydrophyta and Zygnematophyceae split

For tens of millions of years (Ma) the terrestrial habitats of Snowball Earth during the Cryogenian period (between 720 to 635 Ma before present - Neoproterozoic Era) were possibly dominated by global snow and ice cover up to the equatorial sublimative desert. The most recent time-calibrated phylogenies calibrated not only on plants, but on a comprehensive set of eukaryotes, indicate within the Streptophyta, multicellular Charophyceae evolved in Mesoproterozoic to early Neoproterozoic, while Cryogenian is the time of likely Anydrophyta origin (common ancestor of Zygnematophyceae and Embryophyta) and also of Zygnematophyceae – Embryophyta split. Based on the combination of published phylogenomic studies and estimated diversification time comparisons we found strong support for the possibility Anydrophyta likely evolved in response to Cryogenian cooling, and that later in Cryogenian secondary simplification of multicellular Anydrophytes resulted in Zygnematophyceae diversification. We propose Marinoan geochemically documented expansion of first terrestrial flora has been represented not only by Chlorophyta, but also by Streptophyta – including the Anydrophyta – and later by Zygnematophyceae, thriving on glacial surfaces until today. It is possible multicellular early Embryophytes survived in less abundant, possibly relatively warmer refugia, relying more on mineral substrates allowing retention of flagella-based sexuality. Loss of flagella and sexual reproduction by conjugation evolved in Zygnematophyceae during Cryogenian in a remarkable convergent way as in Cryogenian-appearing zygomycetous fungi. We thus support the concept of the important basal cellular exaptations to terrestrial environments evolved in streptophyte algae and propose this was stimulated by the adaptation to glacial habitats dominating the Cryogenian Snowball Earth. Including the glacial lifestyle in the picture of the rise of land plants increases the parsimony of connecting different ecological, phylogenetic and physiological puzzles of the journey from aquatic algae to the terrestrial floras.