The marine ascomycete genus Haloguignardia occurs endophytically in members of the marine brown algal family Sargassaceae globally. This example of endosymbiosis has been morphologically described: the fungal component internally infects the algal host resulting in prolific cell growth, forming galls composed chiefly of host algal cells but containing fungal reproductive structures and vegetative hyphae. H. irritans induces the formation of galls in the brown algae Cystoseira osmundacea and Halidrys dioica along the Pacific coast from Oregon to Baja California, Mexico. Using culture-independent molecular techniques, I sequenced the 18s rDNA gene region for H. irritans and generated a 18s based taxonomy consistent with the current taxonomy for this morphological species. In order to study intraspecific genetic variation in H. irritans I have sequenced the ITS rDNA (ITS 1, 2 and the 5.8s) regions for five separate gall-tissue samples from Santa Rosa Island in southern California and for five samples from Monterey and Carmel in central California. Intraspecific DNA sequence variation in the ITS regions of H. irritans reveals consistent sequence divergence between sites sampled. The fungal ITS regions for H. irritans total 613 bp in length and contain 40 synapomorphic characters for a total of 6.5% variation in informative loci between southern and central Californian sites. This value is similar to those found for the ITS and other gene regions previously used by researchers investigating species boundaries at the intraspecific level in symbiotic, terrestrial fungi. In addition to ITS 1, 2 and the 5.8s gene regions, I am currently using the 5' end of the EF1a coding region to construct intraspecific genealogies for H. irritans. By comparing these genealogies to each other and to the geographic distribution of samples, I aim to determine if more than one genetic species is present within the morphological species H. irritans.

Key words: 18s rDNA, coevolution, ITS, marine fungi, Sargassaceae, symbiosis