Mesostigma

Mesostigma viride is a species of freshwater green algae. It is now considered to be one of the earliest diverging members of green plants/algae (Viridiplantae).
Earlier studies were unable to resolve the position of the species, and it was often placed as a sister to all other green algae, as one of the basal members of the Streptophyta, or as close to "Chaetosphaeridium". More recent studies agree that "Mesostigma" and "Chlorokybus" form a clade, being the earliest diverging green plants.