Wikipedia
Mesostigmatophyceae
The Mesostigmatophyceae are a monotypic class of green algae containing two species.
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 streptophytes.