Rhopalosolen is a genus of green algae in the class Trebouxiophyceae.

[1] It is found in freshwater habitats, and is epizoic or epiphytic on various substrates such as rotifers, nematodes, cladocerans, copepods, fungal hyphae, plants, or other algae.

Cells contain a single chloroplast lining the inside of the cell; the chloroplast is initially plate-like but may become dissected with age, and divide into multiple pieces during reproduction.

In asexual reproduction, biflagellate zoospores are produced that escape through a tear in the mother cell wall near the apex.

[3] Sexual reproduction has been observed in the type species, R. cylindricus, and is anisogamous.