Watanabea green microalgae (Trebouxiophyceae) inhabiting lichen holobiomes: Watanabea lichenicola sp. nova

SUMMARY Microalgae of the genus Watanabea are widely distributed as free living in soil/subaerial and aquatic habitats. In this study, two Watanabea spp. were isolated from lichen thalli of Buellia zoharyi collected on biocrusts in the Iberian Peninsula and the Canary Islands. To ascertain their taxonomic position and phylogenetic relationships within the genus Watanabea, morphological observations were performed using light and confocal microscopy, combined with molecular analyses based on the phylogeny of small subunit ribosomal region (SSU) and internal transcribed spacer region (ITS) genes and the ITS2 secondary structure. One isolate matches Watanabea acidophila, and the other, which has not been previously reported, is described here as Watanabea lichenicola sp. nov. Both molecular phylogenetic analyses (SSU and ITS) suggest the division of the Watanabea spp. into two well‐supported clades: Watanabea group I and Watanabea group II, to which W. lichenicola and W. acidophila belong, respectively. Furthermore, an exclusive side loop in helix 3 of the ITS2 secondary structure of Watanabea group II reinforces the use of this analysis as a molecular hallmark for this genus. The integrative approaches carried out in this study suggest lichen thalli as a new ecological niche for this genus, either as associated (not primary symbiont), epiphyte and/or endophyte microalgae in Buellia zoharyi holobionts.