| This thesis is an investigation of the systematic status and biogeography of the genus Bangia within the order Bangiales and the subclass Bangiophycidae. DNA sequence analyses of the RuBisCO spacer, rbc L gene and 18S rRNA gene, plus morphometric examination, were used to discern possible biogeographic, phylogenetic and taxonomic trends of the red algal genus, Bangia. No correlation was detected between the molecular and morphological analyses. However, all the freshwater collections were nearly identical, indicating that a particular lineage may exist in freshwater systems. In addition, in karyological analyses, freshwater collections were found to have a distinct chromosome morphology in which there are two relatively larger (1--2 m m) and one very small chromosome (ca. 0.5 m m). Based on these findings and the basal position within 18S rRNA molecular analyses, it is recommended that freshwater collections of Bangia should be under the new generic epithet of Pseudobangia atropurpurea. Biogeographic clusters of marine collections appear to contain disjunctions that may be caused by anthropogenic effects. In analysis of Bangia and Porphyra together, both the 18S rRNA and rbc L genes indicate that the sheet-like thallus of the gametophyte of Porphyra and the filamentous form of the gametophyte of Bangia have evolved on more than one occasion within this lineage. We propose that marine Bangia and Porphyra should be grouped in the common generic name of Bngia in which there are two morphotypes: Porphyra and Filiformia until research can further clarify the status of infrageneric taxa. Relationships within the subclass, Bangiophycideae were examined using sequences of the 18S rRNA gene. The analyses show that the order Bangiales is solidly monophyletic. The Compsopogonales, consisting of two freshwater families, the Compsopogonaceae and Boldiaceae, form a well-supported monophyletic clade. The order Rhodochaetales appears to be unsupportable as a separate taxonomic entity and the family Rhodochaetaceae is reclassified to the order Erythropeltidales. The order Porphyridiales as presently conceived, does not constitute a natural monophyletic grouping. Based on our findings, the Porphyridiales can be divided into three orders: Porphyridiales; Stylonematales with two families, Stylonemataceae and a newly proposed family, the Rhodosoraceae; and the last order, Rhodellatales. The two subclasses of the Rhodophyta, Bangiophycidae and Florideophycidae, are non-monophyletic and all members of the Rhodophyta should be classified in the class Rhodophyceae. |
