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ItemMolecular systematics of siphonous green Algae (Bryopsidales, Chlorophyta)Cremen, Ma. Chiela ( 2018)The evolutionary history of the siphonous green algae (Bryopsidales, Chlorophyta) was investigated using a combination of molecular techniques and phylogenetic inference methods. Analyses of chloroplast genomes of the order revealed the high variability of genome architecture and intron content. Proliferation of nonstandard genes associated with mobile functions (i.e. reverse transcriptase/intron maturase, integrases, etc.) was also observed. Evolutionary relationships of families in the order were investigated by increasing taxon sampling and using chloroplast genome data. The chloroplast phylogenies provided good support for the suborders and most families. Several early branching lineages were also inferred in the Bryopsidineae and Halimedineae. A new classification scheme was proposed for the order, which included the following: establishment of the family Pseudobryopsidaceae fam. nov.; merger of the families Pseudocodiaceae, Rhipiliaceae, and Udoteaceae into a broadly circumscribed Halimedaceae and establishment of tribes for the different lineages found therein; finally, the deep-water genus Johnson-sea-linkia, currently placed in Rhipiliopsis, was reinstated based on the chloroplast phylogenies. Plastid (tufA) and nuclear markers (HSP90) and morphological observations were employed to delimit the Halimeda species found in Western Australia. This facilitated the recognition of Halimeda cuneata and the reinstatement of Halimeda versatilis. Investigation on morphological complexity revealed that simple uniaxial thalli was the ancestral state of the siphonous green algae and was maintained throughout their early evolution. Complex multiaxial thalli evolved afterwards on independent occasions.