4. Discussion
Our study provides the first genome-scale perspective into diversification of the lichen forming fungal genus Niebla – endemic to the Pacific coast of Baja California Sur, Baja California and California, highlighting dynamic speciation in this clade of symbiotic fungi. Our data support the perspective of a species-rich genus, and that many species are indeed sympatric, occurring in close association, while single species populations have also been recognized, mostly near the range limits of the genus (Spjut 1996; Spjut et al., 2020). Although candidate species inferred from genome-scale do not support current phenotype-based species circumscriptions, morphologically similar specimens having the same chemotype collected from distinct localities along the coast of Baja California were consistently delimited as separate species-level lineages using RADseq data, further supporting a model of micro-endemism in Niebla (Spjut et al., 2020). On the other hand, morphological parameters applied to distinguish species could be revised to agree with molecular data, while chemical variation in lichen metabolites need further study such as triterpenes in N. lobulata (Spjut, 1996) that may correlate with species differences (Spjut et al., 2020), and isodivaricatic acid found in type specimens of N. eburnea(Spjut-Rakatondraibe comm., Oct 2016) instead of divaricatic acid as reported for N. homalea from the putative type locality (Zhang et al. 2020). Nevertheless, similar to an earlier study using multi-locus sequence data (Spjut et al., 2020), we found that robust, consistent species delimitations were difficult to infer, even with thousands of RADseq loci. Below we discuss the implications of our findings in relationship to the challenge of species delimitation and characterizing diversity in Niebla.