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Abstract Recent studies have uncovered remarkable diversity inDictyonemas.lat. basidiolichens, here recognized as subtribe Dictyonemateae. This group includes five genera and 148 species, but hundreds more await description. The photobionts of these lichens belong toRhizonema, a recently resurrected cyanobacterial genus known by a single species. To further investigate photobiont diversity within Dictyonemateae, we generated 765 new cyanobacterial sequences from 635 specimens collected from 18 countries. The ITS barcoding locus supported the recognition of 200 mycobiont (fungal) species among these samples, but the photobiont diversity was comparatively low. Our analyses revealed three main divisions ofRhizonema, with two repeatedly recovered as monophyletic (proposed as new species), and the third mostly paraphyletic. The paraphyletic lineage corresponds toR. interruptumand partnered with mycobionts from all five genera in Dictyonemateae. There was no evidence of photobiont‐mycobiont co‐speciation, but one of the monophyletic lineages ofRhizonemaappears to partner predominantly with one of the two major clades ofCora(mycobiont) with samples collected largely from the northern Andes. Molecular clock estimations indicate theRhizonemaspecies are much older than the fungal species in the Dictyonemateae, suggesting that these basidiolichens obtained their photobionts from older ascolichen lineages and the photobiont variation in extant lineages of Dictyonemateae is the result of multiple photobiont switches. These results support the hypothesis of lichens representing fungal farmers, in which diverse mycobiont lineages associate with a substantially lower diversity of photobionts by sharing those photobionts best suited for the lichen symbiosis among multiple and often unrelated mycobiont lineages. 

Lichens collected worldwide for centuries have resulted in millions of specimens deposited in herbaria that offer the potential to assess species boundaries, phenotypic diversification, ecology, and distribution. The application of molecular approaches to historical collections has been limited due to DNA fragmentation, but high-throughput sequencing offers an opportunity to overcome this barrier. Here, we combined a large dataset of ITS sequences from recently collected material and historical collections, obtained through Sanger, 454, or Illumina Sequencing, to test the performance of ITS barcoding in two genera of lichenized Basidiomycota: Cora and Corella. We attempted to generate new sequence data for 62 fresh specimens (from 2016) and 274 historical collections (collected between 1888 and 1998), for a final dataset of 1325 sequences. We compared various quantitative approaches to delimit species (GMYC, bPTP, ASAP, ABGD) and tested the resolution and accuracy of the ITS fungal barcoding marker by comparison with a six-marker dataset. Finally, we quantitatively compared phylogenetic and phenotypic species delimitation for 87 selected Cora species that have been formally described. Our HTS approach successfully generated ITS sequences for 76% of the historical collections, and our results show that an integrative approach is the gold-standard for understanding diversity in this group. 

Abstract Three species of lichenized basidiomycetes in the Dictyonema clade from southeastern North America are described as new to science: Cyphellostereum georgianum , C. jamesianum and Dictyonema lawreyi , all with a crustose-filamentous growth form. Based on ITS sequences, the species form well-supported monophyletic clades in a phylogeny and are represented by at least two specimens each. They are also distinguishable by morphological and anatomical characters. These new findings emphasize the importance of lichenological studies in North America, especially in historically understudied taxonomic groups, such as basidiolichens. This study is dedicated to James D. Lawrey on the occasion of his 70 th birthday.