Unexpected cryptic species among streptophyte algae most distant to land plants

Streptophytes are one of the major groups of the green lineage
(Chloroplastida or Viridiplantae). During one-billion-years of evolution,
streptophytes have radiated into an astounding diversity of uni- and
multicellular green algae as well as land plants. Most divergent from land
plants is a clade formed by Mesostigmatophyceae, Spirotaenia spp., and
Chlorokybophyceae. All three lineages are species-poor and the
Chlorokybophyceae consist of a single described species, Chlorokybus
atmophyticus. In this study, we used phylogenomic analyses to shed light
into the diversity within Chlorokybus using a sampling of isolates across
its known distribution. We uncovered a consistent deep genetic structure
within the Chlorokybus isolates, which prompted us to formally extend the
Chlorokybophyceae by describing four new species. Gene expression
differences among Chlorokybus species suggest certain constitutive
variability that might influence their response to environmental factors.
Failure to account for this diversity can hamper comparative genomic
studies aiming to understand the evolution of stress response across
streptophytes. Our data highlight that future studies on the evolution of
plant form and function can tap into an unknown diversity at key deep
branches of the streptophytes.