Autospores generally remain attached to each other to form colonies, but occasionally detach and develop into single cells; when this happens, the number and arrangement of spines can differ from the typical morphology.

[5] Members of the genus Micractinium are common in a variety of freshwater to brackish habitats, and can tolerate a wide array of temperatures, ranging from 0°C in Antarctica to hot springs over 70°C.

[5] The genus Micractinium was formerly placed in the family Micractiniaceae, characterized by sexual reproduction without the production of zoospores, and colonies covered with bristles.

Molecular phylogenetic studies showed that Micractiniaceae was polyphyletic and that Micractinium was closely related to Chlorella.

[2] Both Chlorella and Micractinium sporopollenin in their cell walls, and have pyrenoids that are transversed by thylakoid membranes and covered in a starch sheath.