The Mesostigmatophyceae are a monotypic class of green algae found within the division charophyta that contains 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 charophytes.