Date of Award


Document Type


Degree Name

Doctor of Philosophy (PhD)


Biological Sciences

First Advisor

Russell L. Chapman


Phylogenetic analyses of nucleotide sequences for the nuclear-encoded small subunit ribosomal RNA (SSU) gene were used to test current hypotheses of relationships within the Corallinales and among the florideophycidaean orders of red algae. Analyses of SSU gene sequences indicate that the order Corallinales includes four major lineages. The Sporolithaceae is resolved as the earliest-diverging lineage within the order and forms the sister group to a monophyletic Corallinaceae. The molecular data also support the monophyly of the subfamilies Melobesioideae and Corallinoideae. The latter subfamily is inferred as sister to a fourth lineage including non-geniculate and geniculate species classified in the subfamilies Mastophoroideae, Metagoniolithoideae, Lithophylloideae, and Amphiroideae. Genicula are inferred to have arisen independently in three separate lineages and are not homologous structures. These results indicate that the common taxonomic practice of separating corallines on the basis of the presence or absence of genicula does not accurately reflect the evolutionary history of the group. Cladistic analysis of SSU gene sequences indicates that the Florideophycidae is a monophyletic taxon comprised, roughly, of two large sister clades. One clade includes all orders possessing pit plugs with two cap layers. Within this assemblage, the orders Corallinales and Rhodogorgonales are inferred to be closely related. The second florideophycidaean clade includes, with the exception of the Gelidiales, those orders in which pit plugs are characterized by the absence of cap layers and the presence of a cap membrane. These results support Pueschel's (1994) contention that: (1) "naked" pit plugs are the plesiomorphic type in the Rhodophyta, (2) all orders possessing pit plugs with two cap layers are derived from a common ancestor, (3) outer cap layers are homologous structures, and (4) domed outer caps and cap membranes are derived features within the two cap layer lineage. Results also indicate that although the inner cap layers found in the Bangiales, Hildenbrandiales, and the two-cap-layer lineage may be homologous, inner caps in the Gelidiales are independently derived.