The curious case of Cladonia luteoalba: no support for its distinction

Cladonia luteoalba shows a specific pattern in chemical variability. Its chemotype coincides with that of the associated Cladonia thalli. This has led to the formation of various hypotheses, but its true nature has never been clarified. We collected C. luteoalba in Central Europe and Norway. The chemotypes were detected by TLC and the mycobionts and photobionts were identified by Sanger sequencing of ITS rDNA. Mycobiont cultures were obtained and Illumina metabarcoding of the fungal ITS1 rDNA region was performed targeting minor mycobionts within the thalli. None of the methods supported C. luteoalba as a distinct Cladonia species. In phylogenetic analyses, it was placed in C. straminea and the C. coccifera agg., following the pattern in chemistry. No minor Cladonia were detected by metabarcoding or cultivation. Thus, C. luteoalba remains enigmatic as our data did not support its distinction as a separate Cladonia species.