Trentepohlia C. Martius.

Trentepohlia is a widespread genus well-known for its ability to form conspicuous yellowish to red, orange or brown macroscopic growths on bark, rocks, or leaves (especially in tropical habitats). The thallus is composed of uniseriate branched heterotrichous filaments (Fig. 21). The cells are cylindrical to rounded, surrounded usually by a thick cell wall and contain usually many discoidal plastids without pyrenoids. Reproduction occurs by isogametes or zoospores (Ettl & Gärtner 2013). Free-living cells produce a large amount of carotenoid pigments as a protective barrier against UV-light irradiation, unlike lichenized cells that differ not only by the quantities of pigments but also by altered morphology (Honegger 1998).

The genus, which currently harbours 54 species (Guiry & Guiry 2022), is polyphyletic and intermixed with Printzina (Rindi et al. 2009; Nelsen et al. 2011; Zhu et al. 2017) and Phycopeltis (Zhu et al. 2017) . Trentepohlia includes many lichen photobiont species-level lineages (Nelsen et al. 2011; Kosecka et al. 2020), among which T. lagenifera is so far the only described species (Hametner et al. 2014). However, this lineage is a polyphyletic complex of cryptic species (Rindi et al. 2009) and, for this reason, it was not considered when searching for articles focused on the diversity of free-living lichen symbionts. Lichenized Trentepohlia species do not form a single clade and many closely-related or identical isolates were obtained both from lichen thalli and free-living populations (Nelsen et al. 2011; Hametner et al. 2014; Zhu et al. 2017; Kosecka et al. 2020). A free-living strain identical to the photobiont of Gyalecta jenensis was shown in Hametner et al. (2014). Moreover, Zhu et al. (2017) report a free-living Trentepohlia strain (SAG 118.80) nested within several identical photobiont strains from China.