Microthamniaceae is a family of green algae in the class Trebouxiophyceae.

Currently, there are two accepted genera within the family, Coleochlamys and Microthamnion.

[1] The two genera are sister to each other in molecular phylogenetic analyses, but share little in common morphologically.

[3] Microthamnion consists of branched filaments of cells, and is common worldwide in freshwater habitats.

Meanwhile, Coleochlamys is an uncommon genus consisting of irregularly club-shaped cells, and is an uncommon, cold-tolerant alga of freshwater or terrestrial habitats.