On p. 778 of their review article, Sasso et al. (2012) mentioned a report on flavonoids as sex pheromones in Chlamydomonas eugametos published by Birch et al. (1953). This work could not be confirmed by others (Ryan, 1955; Tomson et al., 1986); in contrast, it was later shown that gametes of opposite mating type meet via random collision and chemotaxis is not involved in the mating of C. eugametos (Tomson et al., 1986). Therefore, while the occurrence of flavonoids in land plants is well secured, the situation in algae is much less clear and requires more experimentation. Apart from the discussion of flavonoids, the content of the review by Sasso et al. (2012) remains unaffected by this addendum.