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Phylogenetic analysis of the geographically disjunct genus Osmundea Stackhouse (Rhodomelaceae, Rhodophyta)
McIvor, L.; Maggs, C.A.; Guiry, M.D.; Hommersand, M.H. (2002). Phylogenetic analysis of the geographically disjunct genus Osmundea Stackhouse (Rhodomelaceae, Rhodophyta). Constancea 83: [no pag.]
In: Constancea: University of California Electronic Publications in Botany. University of California: Berkeley. ISSN 1559-4041, more
Peer reviewed article  

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  • McIvor, L.
  • Maggs, C.A., more
  • Guiry, M.D., more
  • Hommersand, M.H.

    Despite numerous studies, the phylogeny and taxonomy of much of the Laurencia Lamouroux complex still remains obscure. Previous phylogenetic analyses of the genus Osmundea based on comparative morphology and sequences of the plastid-encoded rbcL gene indicated two potentially phylogenetically informative characters. The presence or absence of secondary pit connections in the epidermis and the shape of spermatangial receptacles (urn-shaped or cup-shaped) were synapomorphies for some clades in European species. Osmundea Stackhouse has a markedly disjunct distribution, being confined to Atlantic and Mediterranean coasts of Europe and Pacific North America. The major goal of this study was to extend taxon sampling to Californian species (the “Spectabilis group”) which show character combinations that differ from any European species. In addition, we investigated whether the basionym Fucus oederi Gunnerus might be available for the taxonomically and nomenclaturally confused species Osmundea ramosissima Athanasiadis. The tribe Laurencieae, represented by Chondrophycus, Laurencia, and Osmundea, was well supported, with Chondrophycus papillosus and the type species of Laurencia, L. obtuse, positioned basally. All species currently placed in the genus Osmundea formed a monophyletic group with robust support. Within Osmundea, three clades representing different geographical areas were observed (North Pacific, Atlantic Europe, Mediterranean + Atlantic Europe), with good (91% to 100%) bootstrap support. This phylogeny is interpreted as indicating that the genus may have originated in the late Tethys. The Californian clade and the European Osmundea clades exhibit contrasting stability of characters. The Californian species showed a fixed urn-shaped spermatangial receptacle shape and showed a variable number of epidermal secondary pit connections. In contrast, among the European species, the shape of the spermatangial receptacle shows character reversals and appears to be actively evolving in Mediterranean species. The two distinct European clades of Osmundea are clearly separable by the presence or absence of secondary pit connections. This comparative biogeographical approach to a morphological/molecular phylogenetic investigation has therefore yielded results that challenge the use solely of morphological characters for future generic subdivision in Osmundea.

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