Mesostigma

Mesostigma is a genus of unicellular biflagellate freshwater green algae, with a single species Mesostigma viride, covered by an outer layer of basket‐like scales instead of a cell wall.^[4][3] It is the only known genus in the class Mesostigmatophyceae^[5] (and thus, the only genus in the family Mesostigmataceae^[2] and the order Mesostigmatales^[1]).

Mesostigma
Scientific classification
Clade:	Viridiplantae
Division:	Charophyta
Class:	Mesostigmatophyceae
Order:	Mesostigmatales Marin & Melkonian[1]
Family:	Mesostigmataceae Marin & Melkonian[2]
Genus:	Mesostigma Lauterborn[3]
Species
M. viride Lauterborn

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, close to Chaetosphaeridium.^[6][7][8] More recent studies agree that Mesostigma and Chlorokybus form a clade, being the earliest diverging of the green plants, specifically within Charophytes.^{[9][10][11][12]}