Nucleotide sequences of the nuclear, small-subunit (SSU) ribosomal RNAs, as inferred from polymerase chain reaction (PCR)-amplified products, are presented for Areschougia congesta (Turner) J. Agardh (Solieriaceae), Dasyphloea insignis Montagne (Dumontiaceae), Sarcothalia crassifolia (C. Agardh) Edyvane & Womersley (Gigartinaceae), Nizymenia australis Sonder (Nizymeniaceae), Phacelocarpus peperocarpos (Poiret) Wynne, Ardré & Silva (Phacelocarpaceae), Plocamiocolax pulvinata Setchell, Plocamium angustum (J. Agardh) J.D. Hooker, Plocamium cartilagineum (Linnaeus) Dixon (Plocamiaceae), Rhodymenia linearis J. Agardh (Rhodymeniaceae), and Sphaerococcus coronopifolius Stackhouse (Sphaerococcaceae). Phylogenetic analyses of the SSU sequences between the Plocamiaceae and members of the Sphaerococcaceae, Phacelocarpaceae, and Nizymeniaceae, with which the Plocamiaceae has been associated historically, show SSU differences of between 87 and 105 nucleotides and do not indicate a close relationship. A review of anatomical knowledge of the Plocamiaceae and Pseudoanemoniaceae and new information on vegetative and tetrasporangial development in Plocamium and Plocamiocolax are presented to buttress a case for the Plocamiales ord.nov. Representatives of the Nizymeniaceae and Phacelocarpaceae differ from one another by only nine nucleotides, suggesting that these two taxa are very closely related and perhaps not distinct at the family rank. Key words: Gigartinales, PCR, phylogeny, Plocamiales ord.nov., Pseudoanemoniaceae, Rhodophyta, small-subunit rRNA, systematics.

Appreciation of the true species diversity of the genus Ulva in Australian waters has been blinkered by the unproved assumption that its representatives there are largely cosmopolitan. As species of Ulva are some of the longest‐standing and most widely reported taxa of macroalgae, the presumption that they are worldwide in distribution has led to most Australian members being equated with species originally described from extra‐Australian type localities. Ulva species can be notoriously difficult to identify due to the few and often variable characters on which classical taxonomic studies focus so that names of specimens in hand, as well as names appearing in historical distribution records, are frequently difficult or impossible to verify. The combination of morphological and molecular analyses, the latter involving both nuclear (internal transcribed spacer [ITS]) and plastid (rbcL) markers, is critically important in taxonomic studies of the genus and has here been applied to selected Ulva populations from mostly cool‐temperate southern Australian localities. It has been determined that habit‐ and anatomy‐based keys of standard taxonomic literature are largely adequate for assigning species names based on classical concepts, but they often obscure a number of cryptic and pseudocryptic species that do not conform to extra‐Australian populations of the same designation, as indicated by the corresponding molecular data. Here, we present six species (Ulva australis Aresch., U. compressa Forssk., U. fasciata Delile, U. intestinalis L., U. laetevirens Aresch., U. tanneri H. S. Hayden et J. R. Waaland) for which anatomical and molecular data were congruent with both classical concepts and GenBank accession data and confirm these as cosmopolitan taxa in Australia. We also present six putative species designations based on anatomy [U. clathrata (Roth) C. Agardh, U. flexuosa Wulfen, U. linza L., U. prolifera O. F. Müll., U. stenophylla Setch. et N. L. Gardner, U. brisbanensis sp. nov.] that are inconsistent with molecular data, suggesting novel or cryptic taxa not represented in GenBank.

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Nucleotide sequences of the nuclear, small-subunit ribosomal RNAs, as inferred from polymerase chain reaction amplified products, are introduced for representatives of the Dumontiaceae, Endocladiaceae, Halymeniaceae, and Kallymeniaceae of the order Cryptonemiales sensu Kylin, the Mychodeaceae, Phyllophoraceae, Schizymeniaceae, and Sebdeniaceae of the order Gigartinales sensu Kylin, and the Lomentariaceae and Rhodymeniaceae of the order Rhodymeniales. The new sequences are included in phylogenetic analyses incorporating previously published sequences from additional families of the orders Ahnfeltiales, Ceramiales, Gigartinales, Gracilariales, Palmariales, Plocamiales, and Rhodymeniales. We used the molecular data to test the validity of the taxonomic merger of the orders Gigartinales and Cryptonemiales that was proposed by G.T. Kraft and P.A. Robins in 1985. With only two exceptions (the families Halymeniaceae and Sebdeniaceae), phylogenetic analyses of the SSU data support a monophyletic origin for a combined Gigartinales–Cryptonemiales. We therefore propose the resurrection of a redefined Cryptonemiales to consist, at this time, of only the Halymeniaceae and Sebdeniaceae. Because virtually no elements of the original or recent definitions of the Cryptonemiales survive in the characterization of this taxon, we followed procedures allowed by the International Code of Botanical Nomenclature to designate it the Halymeniales ord.nov. Analysis of molecular data further indicates that the Rhodymeniales is a monophyletic assemblage distinct from both the Gigartinales and Halymeniales; it should not be merged with the Gigartinales as is occasionally suggested. Keywords: Cryptonemiales, Gigartinales, Halymeniaceae, Halymeniales, phylogeny, Rhodophyta, Sebdeniaceae, small-subunit rRNA, systematics.

The recognition of broad biogeographic provinces provides an important framework for ecological and conservation biological research. Marine biologists have long recognized distinct biogeographic provinces in southern Australia, primarily on the basis of qualitative differences in intertidal species assemblages. Here we provide an a priori test for these traditional eastern (Peronian), western (Flindersian) and south-eastern (Maugean) provinces. Specifically, we analyse distributional data for approximately 1500 algal species using the newly available Australian Virtual Herbarium, an online database of herbarium specimens. Our quantitative algal analyses across southern Australia identify three distinct biogeographic assemblages, consistent with traditional qualitative provinces. We argue that these broad provinces provide a highly effective framework for understanding and managing Australia's marine biodiversity. In particular, biogeographic provinces provide a regional framework for integrating the ongoing discovery of biological variation at finer scales. More broadly therefore we recommend that biologists undertake quantitative analyses to test provincial biogeographic boundaries around the globe.