Phylogeny of the Characeae (Charophyta) and Biogeography of Chara (Characeae) Inferred From Ribosomal RNA Genes.
Date of Award
Doctor of Philosophy (PhD)
Russell L. Chapman
This dissertation examined generic, subsection, and infraspecific aspects of the phylogeny of the Characeae, and biogeography of Chara subsections and Chara haitensis. These relationships were inferred from cladistic and maximum likelihood analyses of sequence data for 18S and ITS regions of nuclear-encoded ribosomal RNA genes. Morphologically-based phylogenetic hypotheses of Wood and Imahori (1965) and Khan and Sarma (1984) concerning the six extant members of Characeae were tested. The analyses supported: monophyly of family Characeae, tribe Chareae, and of Lamprothamnium; placement of Nitellopsis basal to tribe Chareae; and an unresolved relationship between Lamprothamnium and Chara. Neither the hypothesis of Wood and Imahori nor that of Khan and Sarma was strongly supported. Morphology-based hypotheses concerning relationships among Chara subsections by Wood and Imahori (1965) and Proctor (1980) were tested. Analyses strongly refute Wood and Imahori's emphasis placed on traditional stipulode and cortication characters as phylogenetically informative. Subsections and species of different stipulode and/or cortication characters may be very closely related to each other (ex. Chara hydropitys, C. brittonii, etc.), because stipulodes and/or cortication can be lost without affecting the other character. Lamprothamnium was strongly supported as being within Chara as some authors have suggested (Wood and Imahori 1965). Proctor's biogeographic hypothesis regarding a basic subsection split along a Laurasian or Gondwanan origin is strongly supported. The biogeography of Chara haitensis, a monoecious member of subsection Willdenowia was examined to determine whether isolates from North and Central America showed a strictly geographic relationship. The patchwork pattern of relationships found did not follow a strict regional relationship as would be expected if migrating birds or other dispersal agents, as suggested by Proctor (1959, 1962, 1966), had no effect. Further examination of the monophyly of Nitella and tribe Nitelleae, the exact relationship between Chara and Lamprothamnium, identification of new phylogenetically informative morphological characters, and a method to link extant species with fossil data would provide a fuller understanding of this distinctive genus. This study complements other molecular studies (McCourt et al. 1996) and has furthered our understanding of this important assemblage of green algae.
Meiers, Susan T., "Phylogeny of the Characeae (Charophyta) and Biogeography of Chara (Characeae) Inferred From Ribosomal RNA Genes." (1997). LSU Historical Dissertations and Theses. 6583.