Figure 2.

Eukaryotic tree of life (Adl et al., 2019; Burki et al., 2020). Rhythms have been identified in most of the subkingdoms of eukaryotes (colored cycling circles near the organism group). However, only a few of these rhythms have been shown to be endogenous to the organisms themselves (although possibly all these organisms have endogenous clocks), and in even fewer the actual circadian clock genes have been identified (purple cycling circle). Euglenids are free-living, aquatic flagellates; Trypanosomatids are eukaryotic parasites; Chlorarachniophytes are a small group of marine algae; Apicomplexa is a group that includes many parasites including Plasmodium, which causes malaria [it has been recently shown to have an endogenous clock (Rijo-Ferreira et al., 2020; Smith et al., 2020)]; Gonyaulax is a genus of dinoflagellates that are aquatic organisms with two separate flagella; Nannochloropsis are microalgae living in freshwater and seawater that are related to diatoms and brown algae.