Mesostigmatophyceae
The Mesostigmatophyceae are a class of basal green algae found in freshwater originally containing two species in a single genus, Mesostigma. Now, a clade containing Chlorokybus and Spirotaenia has been added.. The Mesostigmatophyceae are either places as sister to all other green algae, or more conventially as sister to all Streptophyta.
