Anydrophytes
Anydrophytes are an extinct group named by Rensing (2020) and expanded upon in Žárský et al. (2022)
These were a Cryogenian group of early terrestrial or glacier-bound green algae that had adaptations to tolerate drying out, temperature extremes, light extremes, and UV radiation (Delwiche & Cooper, 2015; de Vries & Archibald, 2018; Rensing, 2020)
They may have had a parenchymatous morphology similar to Coleochaete.
This group is the common ancestor of the zygnematophyte algae and the true land plants (embryophytes)
"Molecular data models extend the possible timing for the origin of the anydrophytes and phylogenetic split between Zygnematophyceae and Embryophyta to either the Mesoproterozoic to early Neoproterozoic (Su et al., 2021), the Cryogenian (Strassert et al., 2021), or the Ediacaran/Cambrian (Morris et al., 2018a)"
Above: An image of Coleochaete which may have been similar in form to the anydrophytes
Above: Rensing (2020), Figure 1 showing a phylogenetic tree of the Viridiplantae clade including the placement of the anydrophytes.
Above: Žárský et al. (2022), Figure 3 showing the hypothetical origins of anydrophytes during the Cryogenian
Terrestrialization by algae and plants
Plant terrestrialization or land plant evolution started most probably with unicellular streptophytes in the late Mesoproterozoic or the Tonian before complex multicellularity evolved (Stebbins and Hill, 1980; Becker, 2013; Harholt et al., 2016)
The streptophyte algae were living on the land for some time before the emergence of land plants (Harholt et al., 2016)
Complex multicellularity in streptophytes probably arose in the early Neoproterozoic (Tonian) into the Cryogenian, and the anydrophytes arose from this ancestor (closely related to Coleochaete)
Over tens of millions of years, the prevalently freezing Cryogenian environments shaped plant cellular adaptations, and these adaptations turned to exaptations in the embryophytes exposed to terrestrial conditions and their transition to the dry land
The physical, physiological, and molecular stresses imposed by desiccation have similar consequences on the plants exposed to freezing stresses
Studies of embryophytes and streptophyte algae indicate a tight coupling between the adaptation to high irradiation and cold and drought stress (e.g., de Vries et al., 2017, 2018; Chen X. et al., 2021).
The cold-adapted early zygnematophytes became reduced from parenchymatous to unicellular and filamentous forms as an adaptation to survival on glaciers
The early embryophytes were not reduced and kept flagellated sex cells, probably surviving on exposed soils.
FIGURE 1 | (A) The phylogenetic tree with time estimates for the splits of Chlorophyta–Streptophyta and Zygnematophyceae–Embryophyta. Tree adapted from Morris et al. (2018b), projected over a timescale based on an international geostratigraphic chart (2020). The red lines at the respective node represent 95% highest posterior densities of estimates presented by Hedges et al. (2018), Morris et al. (2018b), Strassert et al. (2021), and Su et al. (2021): a–Streptophyta, Morris et al. (2018b) all calibrations, b–Streptophyta, Hedges et al. (2018) Mesozoic calibrations, c–Streptophyta, Hedges et al. (2018) Spermatophyta calibration, d–Streptophyta, Strassert et al. (2021), e–Embryophyta, Morris et al. (2018b) all calibrations, f–Embryophyta, Hedges et al. (2018) Mesozoic calibrations, g–Embryophyta, Hedges et al. (2018) Spermatophyta calibration, h–Embryophyta, Su et al. (2021), Strassert et al. (2021). j–Influx of terrestrial carbon is apparent in carbonates younger than 850 Ma, according to a study of Knauth and Kennedy (2009), who infer an explosion of photosynthesizing communities on late Precambrian land surfaces.
(B) Schematic presentation of the potential freshwater habitats in a low latitude Cryogenian catchment. The picture represents habitats populated by members of streptophyte algae in the current biosphere (A) Lentic habitats (Mesostigma, Chara), (B) fluvial habitats with various Zygnematophyceae in the phytobenthos and e.g., Coleochaete on submerged surfaces, (C) subaeric habitats, moist or periodically submerged surfaces, and biological soil crusts (e.g., Klebsormidium, Chlorokybus, and some Zygnematophyceae).
