Undulifilum Škaloud, Černajová & Schiefelbein.

Undulifilum forms heterotrichous, brush-like thalli composed of irregularly branched uniseriate filaments, that are typically regularly undulating or curved (Fig. 28). The filaments are built out of long cylindrical cells with a single, parietal chloroplast possessing a pyrenoid. In mature thalli, the terminal cells of the branches are often significantly longer. Reproduction occurs by vegetative division. Other modes of reproduction have not been observed. The only described species U. symbionticum lives as a photobiont of Verrucariaceae lichens on seashore rocks (Černajová et al. 2022).