The systematics and evolution of the lichen genus Ramalina with an emphasis on the Ramalina americana complex

LaGreca, Scott

A phylogenetic study of lichens of the genus Ramalina, including specimens collected from GRSM. Do lichen chemotypes represent sibling species, or are they polymorphisms within single, chemically variable species? The present study examines this question using the Ramalina americana chemotype complex as a model system. This complex comprises an incredible array of 15 chemotypes, of which six are described here as new. The northern half of the species range is mostly acid-deficient, while the southern half contains almost all of the chemical diversity. Spermagonia and spermatia of R. americana are described for the first time. Like the ascospores, they are produced abundantly by almost every chemotype, but they are not useful for distinguishing them. The presence of spermatia, however, indicates that these lichens, which were once thought to reproduce via obligate homothallism, are capable of outcrossing. This capability is confirmed by a gene-flow study in which two spores of the 4-0-methylhypoprotocetraric chemotype were produced by a maternal thallus of the lecanoric/evernic chemotype. This demonstrates at least a one-way gene-flow between these two chemotypes, and is a first step in delimiting biological species within this complex. A cladistic analysis of rDNA ITS sequences from nineteen individuals representing eight chemotypes reveals that R. americana comprises at least two cryptic, phylogenetic species. One, R. americana, is northern and largely acid-deficient; the other, R. culbersoniorum sp. nov., is southern and encompasses most of the chemical diversity. An analysis involving 16 additional Ramalina species shows that these may not be sister species, but R. intermedia is sister to the northern species. Further, R. fastigiata, R. paludosa, and R. sinensis, often assumed to be closely related to the complex, are probably only distantly related. In addition, five species from the southeastern United States Coastal Plain form a group, and the R. siliquosa complex segregates into two distinct groups (hypoprotocetraric and norstictic/stictic). Analyses of sequences from introns from position 1516 of the SSU rDNA largely support the segregation ofR. culbersoniorum from R. americana, and the close relationship of R. intermedia to the latter species. Analyses of introns from position 1512, the first introns reported from this position in fungi, indicate that R. paludosa and R. willeyi are sister species.