Phylogenetic position of the Sphaeropleaceae (Chlorophyta)

 The complete 18S rRNA gene sequences of four Sphaeroplea C.A. Agardh strains (Sphaeropleales, Sphaeropleaceae), two Atractomorpha Hoffman strains (Sphaeropleales, Sphaeropleaceae) and two Ankyra Fott strains (Chlorococcales, Characiaceae) were determined and subjected to phylogenetic analyses. The analyses indicated that all these taxa belong to a monophyletic lineage (Sphaeropleaceae) and are related to a group of chlorophycean algae comprising autosporic taxa and taxa that reproduce by zoospores which are characterized by directly opposed basal bodies. The taxonomic assignment of the Sphaeropleaceae as a family within the Sphaeropleales (Chlorophyta, Chlorophyceae) is discussed. Received December 22, 2000 Accepted September 25, 2001     

Zur Taxonomie einer auxotrophen Chlorella aus Paramecium bursaria Ehrbg

Zusammenfassung Auf Grund der physiologischen Merkmale einer in Paramecium bursaria Ehrbg. auftretenden Chlorella ergibt sich eine systematische Zuordnung in den Formenkreis um Chlorella vulgaris f. tertia Fott et Nováková und Chlorella vulgaris var. vulgaris Beijerinck. Hiervon abweichende Befunde anderer Autoren werden diskutiert.

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On the taxonomy of an auxotrophic Chlorella isolated from Paramecium bursaria ehrbg

An auxotrophic Chlorella has been isolated from Paramecium bursaria Ehrbg. and cultivated in mass culture in an inorganic medium supplied with vitamins B₁ and B₁₂. With regard to its physiological properties it is not identical with either one of the so far known Chlorella species. It belongs, however, to the group of Chlorella vulgaris f. tertia Fott et Novaková and Chlorella vulgaris var. vulgaris Beijerinck.

     

Physiologische und biochemische Beiträge zur Taxonomie der Gattung Chlorella

Zusammenfassung Die 15 verfügbaren Stämme von Chlorella vulgaris f. tertia Fott et Nováková (früher als Chlorella III, zwei auxotrophe Stämme als Chlorella VI, bezeichnet), die im Gegensatz zu Chlorella vulgaris Beijerinck Hydrogenase enthalten, wurden auf Thermophilie geprüft. Sie erwiesen sich sämtlich als thermophil und erreichen die obere Grenze des Wachstums bei 38–42°C. Damit erscheinen die beiden klassischen Hochtemperatur-Chlorellen (die Stämme 7-11-05 und 1-9-30 von Sorokin) als Angehörige eines ziemlich weit verbreiteten thermophilen Taxons. Unter den 19 verfügbaren Stämmen von Chlorella vulgaris wurden demgegenüber keine Hochtemperatur-Stämme gefunden. Auch bei C. homosphaera, C. fusca var. rubescens, C. luteoviridis, C. zofingiensis, C. sacharophila, C. minutissima und C. protothecoides konnten wir keine thermophilen Stämme nachweisen, während sich bei C. fusca und C. kessleri eine leichte Tendenz zur Thermophilie zeigte. Chlorella vulgaris f. tertia ist somit anscheinend ein Taxon ökologischer Spezialisten, die zu einer Existenz bei erhöhten Temperaturen, unter anaeroben Bedingungen oder auch als Symbionten in Tieren (zwei Stämme sind Zoochlorellen aus dem Süßwasser-Schwamm Spongilla) befähight sind. Wir nehmen an, daß es sich dabei um eine primitive, phylogenetisch alte Gruppe von Organismen handelt, aus der sich die morphologisch gleiche, typische Chlorella vulgaris durch den Verlust von Hydrogenase und Thermophilie entwickelt haben könnte.

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Physiological and biochemical contributions to the taxonomy of the genus Chlorella VII. The thermophily of Chlorella vulgaris f. tertia Fott et Nováková

Summary The 15 available strains of Chlorella vulgaris f. tertia Fott et Nováková (previously designated as Chlorella III, two auxotrophic strains as Chlorella VI) contain hydrogenase, in contrast to Chlorella vulgaris Beijerinck. In addition, all strains of C. vulgaris f. tertia were now found to be thermophilic, i.e., able to grow at up to 38–42°C. Thus the two classical high-temperature Chlorellae (strains 7-11-05 and 1-9-30 of Sorokin) appear as members of a rather common thermophilic taxon. Among the 19 available strains of Chlorella vulgaris, by contrast, no hightemperature strains were observed. Likewise, we did not find any thermophilic strains of C. homosphaera, C. fusca var. rubescens, C. luteoviridis, C. zofingiensis, C. saccharophila, C. minutissima, and C. protothecoides. C. fusca and C. kessleri, on the other hand, show a slight tendency towards thermophily. Chlorella vulgaris f. tertia therefore seems to be a taxon of ecological specialists, equipped for the existence at elevated temperatures, in anaerobic environments, or as symbionts in animals (two strains are Zoochlorellae isolated from the fresh-water sponge, Spongilla). We assume that it represents a primitive, phylogenetically old group of organisms. The morphologically identical, typical Chlorella vulgaris might have evolved from it through loss of hydrogenase and thermophily.

     

STEROL,FATTY ACID,AND PIGMENT CHARACTERISTICS OF UTEX 2341, A MARINE EUSTIGMATOPHYTE IDENTIFIED PREVIOUSLY AS CHLORELLA MINUTISSIMA (CHLOROPHYCEAE)1

An examination of the sterols of UTEX 2341, a small (ca. 2μm), nonmotile unicellular marine alga identified as Chlorella minutissima Fott et Novakova, yielded results inconsistent with any of 35 Chlorella strains analyzed previously. UTEX 2341 contained cholesterol as the principal sterol, with 24-methylenecholesterol, fucosterol, and isofucosterol also present; these are not dominant sterols in any other Chlorella species. Presence of eicosapentaenoic acid in UTEX 2341 also contrasted with fatty acids of Chlorella strains analyzed previously. Pigment analysis of UTEX 2341 revealed that it contained chlorophyll a, but not chlorophylls b or c; violaxanthin was the only major xanthophyll pigment. Both lipid and pigment compositions suggest that UTEX 2341 is not a member of the genus Chlorella but, rather, belongs in the Eustigmatophyceae; it may be Nannochloropsis sp. Cells with possible extracellular structures were present at an appreciable percentage of the stationary-phase population studied; centrifuging removed or collapsed these structures. The high cholesterol and polyunsaturated fatty acid contents of UTEX 2341 make it attractive as a potential aquaculturefeed, provided it is, or can be made, digestible.     

Phylogenetic position of endosymbiotic green algae in Paramecium bursaria Ehrenberg from Japan

Endosymbiotic green algae of Japanese Paramecium bursaria were phylogenetically analyzed based on DNA sequences from the ribosomal DNA operon (18S rDNA, ITS1, 5.8S rDNA, and ITS2). Phylogenetic trees constructed using 18S rDNA sequences showed that the symbionts belong to the Chlorella sensu stricto (Trebouxiophyceae) group. They are genetically closer to the C. vulgaris Beijerinck group than to C. kessleri Fott et Nováková as proposed previously. Branching order in C. vulgaris group was unresolved in 18S rDNA trees. Compared heterogeneities of 18S rDNA, ITS1, 5.8S r, and ITS2 among symbionts and two Chlorella species, indicated that the ITS2 region (and probably also ITS1) is better able to resolve phylogenetic problems in such closely related taxa. All six symbiotic sequences obtained here (approximately 4000-bp sequences of 18S rDNA, ITS1, 5.8S rDNA, and ITS2) were completely identical in each, strongly suggesting a common origin.     

BIOCHEMICAL TAXONOMY AND MOLECULAR PHYLOGENY OF THE GENUS CHLORELLA SENSU LATO (CHLOROPHYTA)

A multimethod approach was used to characterize unicellular green algae that were traditionally assigned to the genus Chlorella Beijerinck and to resolve their phylogenetic relationships within the Chlorophyta. Biochemical, physiological, and ultrastructural characters, together with molecular data such as DNA base composition and DNA hybridization values, were compared with a molecular phylogeny based on complete 18S rRNA sequences. Our results show that Chlorella taxa are dispersed over two classes of chlorophytes, the Trebouxiophyceae and the Chlorophyceae. We propose that only four species should be kept in the genus Chlorella (Chlorophyta, Trebouxiophyceae): C. vulgaris Beijerinck, C. lobophora Andreyeva, C. sorokiniana Shih. et Krauss, and C. kessleri Fott et Nováková. Common characteristics of these taxa are glucosamine as a dominant cell wall component and the presence of a double thylakoid bisecting the pyrenoid matrix. Norspermine, norspermidine, and secondary carotenoids are never produced. Other "Chlorella" species belong to different taxa within the Trebouxiophyceae ( "C." protothecoides = Auxenochlorella protothecoides [Krüger] Kalina et Punčochářová, "C." ellipsoidea, "C." mirabilis, "C." saccharophila, and "C." luteoviridis ) and Chlorophyceae ( "C." zofingiensis and "C." homosphaera = Mychonastes homosphaera Kalina et Punčochářová). The latter taxa can easily be recognized by the production of secondary carotenoids under nitrogen-deficient conditions.     

DISCONTINUOUS MITOCHONDRIAL AND CHLOROPLAST LARGE SUBUNIT RIBOSOMAL RNAs AMONG GREEN ALGAE: PHYLOGENETIC IMPLICATIONS1

To provide insights into the occurrence, evolution, and phylogenetic distribution of discontinuous mitochondrial and chloroplast large subunit ribosomal RNAs (LSU rRNAs) among green algae, we surveyed 12 taxa representing three classes of green algae: the Chlorophyceae, Pleurastrophyceae, and Micromonadophyceae (sensu Mattox and Stewart 1984). We present evidence that discontinuous mitochondrial and chloroplast LSU rRNAs are quite widespread among green algae. Mitochondrial LSU rRNAs appear discontinuous in zoosporic chlorophycean lineages displaying a clockwise or directly opposed configuration in their flagellar apparatus, as well as in chlorococcalean autosporic taxa phylogenetically related to them, but are continuous among zoosporic green algal lineages with a counterclockwise flagellar apparatus configuration, as well as among chlorococcalean autosporic taxa phylogenetically related to them. Chloroplast LSU rRNAs appear discontinuous in all of the lineages investigated. Discontinuous mitochondrial LSU rRNA represents a molecular trait that might have originated at or near the base of Chlorophyceae, whereas discontinuous chloroplast LSU rRNA might have developed very early in the evolutionary history of the green algal group itself. We suggest, therefore, that the presence of discontinuous mitochondrial but not chloroplast LSU rRNA can be used as an additional character in assessing phylogenetic affiliations among green algae.     

Physiologische und biochemische Beiträge zur Taxonomie der Gattung Chlorella

Zusammenfassung Es wurde die Verwendbarkeit von Acetat, Glucose, Fructose, Galactose, Saccharose und Lactose als Kohlenstoffquelle für das Wachstum von 72 Chlorella-Stämmen, die 10 autotrophen Taxa angehören, untersucht. Im Dunkeln zeigen mit Acetat 34 Stämme und mit Glucose 37 Stämme gutes Wachstum (Chlorella kessleri, die meisten Stämme von C. vulgaris und C. vulgaris f. tertia, sowie einige wenige Stämme von C. fusca), während Fructose von 21 Stämmen verwertet wird (C. kessleri, die meisten Stämme von C. luteoviridis und C. saccharophila, sowie einige Stämme von C. fusca und C. zofingiensis). Gutes Wachstum mit Galactose wurde bei 11 Stämmen gefunden (C. kessleri und einige Stämme von C. vulgaris). Saccharose und Lactose ermöglichen dagegen kein intensives Wachstum. Die Verwendbarkeit der 6 geprüften organischen Verbindungen für heterotrophes Wachstum ist als taxonomisches Merkmal zur Charakterisierung von Chlorella-Arten nicht geeignet. Lediglich Chlorella kessleri Fott et Nováková, die allgemein die ausgeprägteste Fähigkeit zu heterotrophem Wachstum besitzt, unterscheidet sich durch gute Verwertung von Galactose von den übrigen Arten.

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Physiological and biochemical contributions to the taxonomy of the genus Chlorella VI. Utilization of organic carbon compounds

Summary The utilization of acetate, glucose, fructose, glactose, saccharose, and lactose as sources of carbon for growth in the dark of 72 Chlorella strains belonging to 10 autotrophic taxa was studied. 34 strains grow well with acetate and 37 strains with glucose (Chlorella kessleri, most strains of C. vulgaris and C. vulgaris f. tertia, and a few strains of C. fusca), and fructose is utilized by 21 strains (C. kessleri, most strains of C. luteoviridis and C. saccharophila, and some strains of C. fusca and C. zofingiensis). 11 strains show good growth with galactose (C. kessleri and some strains of C. vulgaris). Saccharose and lactose, on the other hand, do not support vigorous growth. Utilization of the 6 organic compounds cannot serve as a taxonomic character in the genus Chlorella. However, Chlorella kessleri Fott et Nováková shows the most pronounced ability for heterotrophic growth and differs in its good growth with galactose from the other species.

     

Interesting taxa ofStaurastrum Meyen (Desmidiaceae) from Karnataka State (India)

Algae were collected from a paddy field at Belgaum during August 1985. Two new taxa ofStaurastrum Meyen (viz.S. quebecense Irénée-Marie fa.minor Bongale fa.nov. andS. sebaldii Renisch var.triangularis Bongale var. nov.) and two other taxa showing major variations (viz.S. gracile Ralfs. var.elongatulum West et West fa. andS. leutkemuelleri Donat et Ruttner ms. fa.) are reported.     

Molecular characterization of Chlorella cultures of the National Institute for Environmental Studies culture collection with description of Micractinium inermum sp. nov., Didymogenes sphaerica sp. nov., and Didymogenes soliella sp. nov. (Chlorellaceae,Trebouxiophyceae)

Chlorella Beijerinck (Chlorellaceae, Trebouxiophyceae) strains from the collection of the National Institute for Environmental Studies (NIES) were characterized using gene sequence data. The misidentification of a number of strains was rectified. Chlorella vulgaris Beijerinck NIES‐2173 was reclassified as C. sorokiniana Shihira et Krauss. Chlorella sp. NIES‐2171 was described as a new species in the genus Micractinium Fresinius, M. inermum Hoshina et Fujiwara. Chlorella sorokiniana NIES‐2167 and Chlorella sp. NIES‐2330 were found to be phylogenetically related to Didymogenes Schmidle. We propose these two strains be transferred to the genus Didymogenes and given new names: D. sphaerica Hoshina et Fujiwara and D. soliella Hoshina et Fujiwara. Taxonomic decisions were primarily based on small subunit‐internal transcribed spacer ribosomal DNA phylogeny for genus assignment and ITS2 sequence‐structure to determine species autonomy. Our findings suggest that this strategy is the most effective way to use the species concept among autosporic coccoids.     

Phylogenetic position of someChlorella species within the chlorococcales based upon complete small-subunit ribosomal RNA sequences

Summary Complete small-subunit rRNA (16S-like rRNA) coding region sequences were determined for eight species of the Chlorococcales (Chlorophyceae). The genera investigated includePrototheca, Ankistrodesmus, Scenedesmus, and fiveChlorella species. Distance matrix methods were used to infer a phylogenetic tree that describes evolutionary relationships between several plant and green algal groups. The tree exhibits a bifurcation within the Chlorococcales consistent with the division into Oocystaceae and Scenedesmaceae, but three of the fiveChlorella species are more similar to other algae than toChlorella vulgaris. All of the sequences contain primary and secondary structural features that are characteristic of 16S-like rRNAs of chlorophytes and higher plants.Anikstrodesmus stipitatus, however, contains a 394-bp group I intervening sequence in its 16S-like rRNA coding region.     

New taxa ofCosmarium Corda (Desmidiaceae) from Karnataka State,India

Six new taxa including two new species (Cosmarium bourrellyi Bongale sp. nov. andC. desikacharyi Bongale sp. nov.) and four new varieties (C. auriculatum var.protrusum Bongale var. nov.,C. pachydermum var.inflatum Bongale var. nov.,C. pseudoconnatum var.tuberculans Bongale var. nov. andC. quadrum var.rotundatum Bongale var. nov.) are reported. Algae were collected from a paddy field at Belgaum.     

18S RIBOSOMAL DNA SEQUENCES INDICATE A MONOPHYLETIC ORIGIN OF CHAROPHYCEAE1

Nuclear-encoded small-subunit (18S) ribosomal RNA genes of Chara australis R. Brown (C. corallina var. nobilis f. nobilis R.D.W.) and Nitella flexilis (L.) Ag. were amplified by polymerase chain reaction, cloned, and completely sequenced. Using structural criteria, the sequences were aligned with 18S ribosomal DNAs (rDNAs) from 11 other chlorophyll b-containing algae and six higher plants (embryophytes). Phylogenetic trees were inferred by distance, neighbor-joining, parsimony, and maximum-likelihood approaches; confidence intervals were estimated by bootstrapping, and nonrandomness of tree structure was confirmed by permutation tests. 18S rDNAs of C. australis and two Nitella species were found to be specifically related and, together with 18S rDNAs of Chlorokybus atmophyticus Geitler, Klebsormidium flaccidum (A. Br.) Silva, Mattox, et Blackwell, and two Coleochaete species, support a robust monophyletic group (Charophyceae). Although most trees favored a specific sister-group relationship between Charophyceae and embryophytes, statistical tests revealed that a sister-group relationship between Charophyceae and Chlorophyceae could not be ruled out. Additional complete sequences from 18S rDNAs of lower land plants may be required to resolve phylogenetic relationships among these organisms.     

Large-subunit rRNA sequence of the chytridiomyceteBlastocladiella emersonii,and implications for the evolution of zoosporic fungi

The 5.8S and 28S ribosomal RNA sequences of the chytridiomyceteBlastocladiella emersonii were determined. These data were combined with 18S rRNA sequences in order to carry out a phylogenetic analysis based on distance matrix, parsimony, and maximum likelihood methods. The new data confirmed that chytridiomycetes are true fungi and not protists, as was already suggested on the basis of biochemical, ultrastructural, and 18S rRNA data. Within the fungal clade,B. emersonii formed the first line of divergence. The position of the fungi within the eukaryotic “crown” taxa was also reassessed, and the alveolate-stramenopile cluster appeared as their sister group. The stramenopiles also comprise a number of zoosporic fungi, which resemble chytridiomycetes in so many respects, e.g., production of motile spores, thallus morphology, and absorptive nutrition, that they have been classified together with them in the past. This suggests that the possible common ancestor of the fungi, stramenopiles, and alveolates may have been a zoosporic fungus, which would mean that zoosporic fungi are paraphyletic instead of polyphyletic as previously suggested. Correspondence to: R. De Wachter     

Differential sensitivity of green algae to allelopathic substances from Chara

Three short-term laboratory experiments were conducted to investigate allelopathic effects of a mixture of Chara globularis var. globularis Thuillier and Chara contraria var. contraria A. Braun ex Kützing on three different green algae. Single phytoplankton species were exposed to filtered water originating from charophyte cultures. Phytoplankton growth was monitored by determination of chlorophyll concentrations in batch cultures. The change in chlorophyll concentration during the experiments was analysed with a logistic growth model, resulting in an estimate of the exponential growth rate and the duration of the lag phase of the single green algae. The results indicate allelopathic effects of Chara on the growth of the green algae Selenastrum capricornutum Printz and Chlorella minutissima Fott et Nováková, whereas Scenedesmus obliquus (Turpin) Kützing did not seem to be affected. The exponential growth rate of S. capricornutum decreased 7% in the presence of water from a charophyte culture, while the growth rate of C. minutissima decreased with 3%. The allelopathic effect of Chara did not increase when the green alga C. minutissima was P-limited. The effect of Chara was different when young sprouts were used. With young sprouts the duration of the lag phase of C. minutissima was extended (25%), whilst for old plants the growth rate of this green alga decreased. Although the inhibiting effect of charophytes on specific phytoplankton species is rather small, the differential sensitivity of the species to Chara might influence the composition and biomass of phytoplankton communities in the field.     

New and interesting desmids (Zygnematales, Chlorophyceae) collected from Brazil and Argentina

The morphology and taxonomy of nine desmid taxa belonging to the three genera Closterium, Euastrum and Cosmarium are studied based on freshwater algal collections from Brazil and Argentina. They represent five new varieties (Closterium cynthia De Notaris var. minutum Kanetsuna var. nov., Euastrum attenuatum Wolle var. saitoi Kanetsuna var. nov., Cosmarium laticollum Delponte var. minutum Kanetsuna var. nov., Cosmarium pseudovariolatum Grönblad var. major Kanetsuna var. nov. and Cosmarium taxichondrum Lundell var. yamagishii Kanetsuna var. nov.), two new forms (Euastrum hypochondrum Nordstedt var. hypochondrum f. divergens Kanetsuna f. nov. and Euastrum insulare (Wittrock) Roy var. silesiacum (Gronblad) Krieger f. brasiliense Kanetsuna f. nov.) and one new status (Cosmarium pseudovariolatum Gronblad var. incrassatum (Scott et Gronblad) Kanetsuna f. elonga‐tum (Scott et Gronblad) Kanetsuna stat. nov.). In addition, a new combination (Cosmarium pseudovariolatum Gronblad var. incrassatum (Scott et Gronblad) Kanetsuna comb, nov.) is proposed.     

DIVERSITY AND PHYLOGENETIC PLACEMENT OF BRACTEACOCCUS TEREG (CHLOROPHYCEAE,CHLOROPHYTA) BASED ON 18S RIBOSOMAL RNA GENE SEQUENCE DATA1

Sequence data from the nuclear small-subunit ribosomal RNA gene was obtained for nine strains of Bracteacoccus Tereg, representing at least five morphological species and four distinct geographic locations. These, along with sequence data from two additional chlorophycean taxa, Spongiochloris spongiosa Starr and Ascochloris multinucleata Bold et MacEntee, and 48 published sequences from green algal taxa, were used to determine the phylogenetic placement of Bracteacoccus with respect to other chlorophycean green algae. Results support the monophyly of Bracteacoccus strains, contrasting with patterns observed so far for many other coccoid green algae. The range of variation among Bracteacoccus strains is similar to that of other congeners. Basal body orientation in Bracteacoccus has been interpreted as clockwise; however, the 18S data point to a relationship between Bracteacoccus and taxa with the directly opposed configuration of the flagellar apparatus. No close relationship was found to the multinucleated green coccoids with clockwise orientation of basal bodies, such as Spongiochloris, or to those with parallel basal bodies, such as Spermatozopsis. However, 18S data confirm that the motile and vegetative cells of Bracteacoccus are structurally distinct from the representatives of sphaeroplealean families currently studied. It is premature to reclassify Bracteacoccus until 18S comparisons can be made with additional sphaeroplealean taxa and with algae with similar flagellar structure such as Dictyochloris and Heterochlamydomonas.     

ESSENTIAL OILS AS TAXONOMIC AIDS IN THE CLASSIFICATION OF DICHANTHIUM PARVIFLORUM

Essential oil components and gross morphological characters are closely correlated in Dichanthium parviflorum (R. Br.) de Wet et Harlan (Gramineae) and related species. Different species, varieties, and geographical races, as well as hybrids between them, can be identified on the basis of absence or presence and quantity of essential oil components. The morphologically variable D. parviflorum was subdivided into four varieties: var. parviflorum, var. capilliflorum (Steud.) de Wet et Harlan comb. nov., var. mutispiculum (Ohwi) de Wet et Harlan comb. nov., and var. spicigerum (S. T. Blake) de Wet et Harlan comb. nov. These varieties differ from each other morphologically in having respectively racemes with 1-4 and awned, 3-5 and awned, 1-2 and awnlass, and 4-10 and awned spikelet pairs per raceme.     

A new forma and a new species of the generaScenedesmus andSiderocelis (Chlorophyceae) from the nannoplankton of a brackish-water coastal pool

Summary Two new taxa of theChlorococcales are described.Siderocelis minor sp. nov. is similar toS. nana Fott & Heynig in releasing 4 autospores from breaks in the cell wall at either end of the autospore mother cell but differs in the arrangement of granules found in the cell wall.Scenedesmus granulatus f.salina f. nov. differs fromSc. granulatus West & West in size and fromSc. costato-granulatus andSc. granulatus var.verruco-costatus (Roll) Dedus in the distribution and form of cell wall granules.     

A preliminary investigation of the order Bangiales (Bangiophycidae, Rhodophyta) based on sequences of nuclear small-subunit ribosomal RNA genes

We investigated phylogenetic relationships among red algae of the order Bangiales by analysis of sequences of the nuclear gene encoding cytosolic small-subunit ribosomal RNA in Bangia atropurpurea (Roth) C. Ag. and eight samples representing seven species of Porphyra. The ssu-rDNA range from 1818 to 1845 nucleotides in length, with guanosine plus cytosine ratios between 47.0% and 48.6%. A group IC1 intron occurs in the B atropurpurea ssu-rDNAs at the same position as in P. spiralis var. amplifolia Oliveira Filho et Coll and several other eukaryote ssu-rDNAs. The nine sequences form a stable monophyletic group upon phylogenetic analysis. The ssu-rDNA from B. atropurpurea nests stably within the Porphyra group and is closely related to P. amplissima (Kjellm.) Setchell et Hus in Hus, making the genus Porphyra paraphyletic. No correlation is seen between phylogenetic position and number of cell layers in the Porphyra thallus. We discuss possible taxonomic and evolutionary implications of these observations.