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Abstract PremiseSouthern Africa is a biodiversity hotspot rich in endemic plants and lichen‐forming fungi. However, species‐level data about lichen photobionts in this region are minimal. We focused onTrebouxia(Chlorophyta), the most common lichen photobiont, to understand how southern African species fit into the global biodiversity of this genus and are distributed across biomes and mycobiont partners. MethodsWe sequencedTrebouxianuclear ribosomal ITS andrbcLof 139 lichen thalli from diverse biomes in South Africa and Namibia. GlobalTrebouxiaphylogenies incorporating these new data were inferred with a maximum likelihood approach.Trebouxiabiodiversity, biogeography, and mycobiont–photobiont associations were assessed in phylogenetic and ecological network frameworks. ResultsAn estimated 43 putativeTrebouxiaspecies were found across the region, including seven potentially endemic species. Only five clades represent formally described species:T. arboricolas.l. (A13),T. cf.cretacea(A01),T. incrustata(A06),T. lynniae(A39), andT. maresiae(A46). Potential endemic species were not significantly associated with the Greater Cape Floristic Region or desert.Trebouxiaspecies occurred frequently across multiple biomes. Annual precipitation, but not precipitation seasonality, was significant in explaining variation inTrebouxiacommunities. Consistent with other studies of lichen photobionts, theTrebouxia–mycobiont network had an anti‐nested structure. ConclusionsDepending on the metric used, ca. 20–30% of globalTrebouxiabiodiversity occurs in southern Africa, including many species yet to be described. With a classification scheme forTrebouxianow well established, tree‐based approaches are preferable over “barcode gap” methods for delimiting new species. 

Abstract Peltigera globulata Miadl. & Magain, a new species in the P. ponojensis/monticola species complex of section Peltigera , is formally described. This clade was previously given the interim designation Peltigera sp. 17. It is found in sun-exposed and xeric habitats at high altitudes in Peru and Ecuador. Peltigera globulata can be easily recognized by its irregularly globulated margins covered mostly by thick, white pruina, somewhat resembling the sorediate thallus margins of P. soredians , another South American species from section Peltigera . The hypervariable region of ITS1 (ITS1-HR), which is in general highly variable among species of section Peltigera , does not have diagnostic value for species identification within the P. ponojensis/monticola complex. Nevertheless, no significant level of gene flow was detected among eight lineages representing a clade of putative species (including P. globulata ) within this complex. ITS sequences from the holotype specimens of P. monticola Vitik. (collected in 1979) and P. soredians Vitik. (collected in 1981) and lectotype specimens of P. antarctica C. W. Dodge (collected in 1941) and P. aubertii C. W. Dodge (collected in 1952) were successfully obtained through Sanger and Illumina metagenomic sequencing. BLAST results of these sequences revealed that the type specimen of P. monticola falls within the P. monticola/ponojensis 7 clade, which represents P. monticola s. str., and confirmed that the type specimen of P. aubertii falls within a clade identified previously as P. aubertii based on morphology. The ITS sequence from the type specimen of P. soredians , which superficially resembles P. globulata , confirms its placement in the P. rufescens clade. Finally, we discovered that the name P. antarctica was erroneously applied to a lineage in the P. ponojensis/monticola clade. The ITS sequence from the type specimen of P. antarctica represents a lineage within the P. rufescens clade, which is sister to the P. ponojensis/monticola clade. 

Summary Powdery mildew is an economically important disease caused byc. 1000 different fungal species.Erysiphe vacciniiis an emerging powdery mildew species that is impacting the blueberry industry. Once confined to North America,E. vacciniiis now spreading rapidly across major blueberry‐growing regions, including China, Morocco, Mexico, and the USA, threatening millions in losses.This study documents its recent global spread by analyzing both herbarium specimens, some over 150‐yr‐old, and fresh samples collected world‐wide.Our findings were integrated into a ‘living phylogeny’ via T‐BAS to simplify pathogen identification and enable rapid responses to new outbreaks. We identified 50 haplotypes, two primary introductions world‐wide, and revealed a shift from a generalist to a specialist pathogen.This research provides insights into the complexities of host specialization and highlights the need to address this emerging global threat to blueberry production.