Phylogenetic placement of the basidiomycetous yeastsKondoa malvinella andRhodosporidium dacryoidum,and the anamorphic yeastSympodiomycopsis paphiopedili by means of 18S rRNA gene sequence analysis

The 18S ribosomal RNA gene sequences of the basidiomycetous yeastsKondoa malvinella andRhodosporidium dacryoidum, and an anamorphic yeastSympodiomycopsis paphiopedili were determined. The 18S rRNA gene ofR. dacryodium IAM 13522 (ex type) revealed the presence of an intron-like region with a length of 404 nucleotides, which is presumably assigned to a group I intron. The phylogenetic tree, including 34 published reference sequences, was inferred from 1493 sites which could be unambiguously aligned. The molecular phylogeny, using the ascomycetes as an outgroup, divided the basidiomycetes into three major lineages. The first lineage was composed of the smut fungi (Ustilaginales), represented byUstilago maydis, U. hordei, andTilletia caries, includingS. paphiopedili. The second lineage included the type species of teliospore-forming yeast generaLeucosporidium, Rhodosporidium, andSporidiobolus, and the generaErythrobasidium andKondoa, both previously included in the Filobasidiaceae.Rhodosporidium dacryodium showed a close relationship withE. hasegawianum, which was backed by a high bootstrap support. The rust fungiCronartium ribicola andPeridermium harknessii were also included in this lineage. The last lineage was formed by the filobasidiaceous yeasts,Cystofilobasidium capitatum, Mrakia frigida, Filobasidium floriforme, andFilobasidiella neoformans, and the anamorphic yeastsBullera alba (the anamorph ofBulleromyces albus) andTrichosporon cutaneum. Members ofTremella and selected hymenomycetous genera were also included in this lineage.The nucleotide sequence data reported in this paper will appear in the GSDB, DDBJ, EMBL and NCBI nucleotide sequence databases with the following accession numbers D13459 (Rhodosporidium dacryodium), D13776 (Kondoa malvinella), and D14006 (Sympodiomycopsis paphiopedili).     

Phylogenetic relationships of Chalara and allied species inferred from ribosomal DNA sequences

The phylogenetic relationships of Chalara and allied taxa are studied based on ribosomal DAN sequences. Partial 28S rDNA and 18S rDNA regions from 26 strains were sequenced in this study. These and related sequences from GenBank were analyzed using parsimony and Bayesian analyses. Most of the Chalara species clustered in a strongly supported monophyletic lineage representing Helotiales. However, a few Chalara species appeared closely related to Xylariales. The phylogenetic significance of morphological characters observed in Chalara species are evaluated based on our sequence analyses. Conidial septation, conidial width and conidiophore pigmentation are thought to be indicative in understanding their evolutionary relationships. Sterile setae, which traditionally have been used to delimitate Chaetochalara from Chalara, are phylogenetically insignificant.     

DNA barcoding in the rust genus Chrysomyxa and its implications for the phylogeny of the genus

Chrysomyxa rusts are fungal pathogens widely present in the boreal forest. Taxonomic delimitation and precise species identification are difficult within this genus because several species display similar morphological features. We applied a DNA barcode system based on the ribosomal internal transcribed spacer region (ITS), large subunit (28S) ribosomal RNA gene, mitochondrial cytochrome oxidase 1 (CO1) and mitochondrial NADH dehydrogenase subunit 6 (NAD6) in 86 strains from 16 different Chrysomyxa species, including members of the Chrysomyxa ledi species complex. The nuclear ITS and 28S loci revealed higher resolving power than the mitochondrial genes. Amplification of the full CO1 barcode region failed due to the presence of introns limiting the dataset obtained with this barcode. In most cases the ITS barcodes were in agreement with taxonomic species based on phenotypic characters. Nevertheless we observed genetically distinct (different DNA barcodes) lineages within Chrysomyxa pyrolae and Chrysomyxa rhododendri, providing some evidence for allopatric speciation within these morphologically defined species. This finding, together with the observed pattern of host specificities of the studied rust fungi, suggest that species diversification within the C. ledi species complex might be governed by a set of factors such as specialisation to certain Ericaceae species as telial hosts and to a lesser extent specialization to different spruce species as aecial hosts. Moreover allopatric speciation by geographic disruption of species also seems to take place. When our data were integrated into a broader phylogenetic framework the Chrysomyxa genus unexpectedly was not resolved as a monophyletic group. Indeed the spruce cone rusts C. pyrolae and C. monesis coalesced with the pine needle rusts belonging to the genus Coleosporium, whereas the microcyclic species Chrysomyxa weirii was embedded within a clade comprising the genus Melampsora.     

Ribosomal RNA sequence comparisons demonstrate an evolutionary relationship betweenZygnematales and charophytes

The nuclear-encoded small subunit ribosomal RNA (rRNA) sequences were determined forGenicularia spirotaenia, Mesotaenium caldariorum, andStaurastrum spec. (Zygnematales) to elucidate the evolutionary position of these green algae. Results of neighbour-joining and maximum parsimony phylogenetic analyses support a monophyletic origin of theZygnematales within the evolutionary assemblage defined by theCharophyceae (sensuMattox & Stewart) and land plants. TheZygnematales/Charophyceae/land plants are evolutionarily distinct from the monophyletic lineage defined by theChlorodendrales, Pseudoscourfieldiales, and theMicrothamniales/Chlorophyceae. In memoriamRobert W. Hoshaw.     

Phylogenetic analysis of Asian<Emphasis Type="Italic"> Symplocos</Emphasis> (Symplocaceae) based on nuclear and chloroplast DNA sequences

Thirty species and one variety of Symplocos (Symplocaceae), including all taxa distributed in Japan, were phylogenetically analyzed with DNA sequence data. The evolution of morphological characters is discussed on the basis of the phylogenetic relationships obtained. All species were Asian, except one, S. austromexicana, from Mexico. The nuclear ribosomal internal transcribed spacer (ITS) region and two intergenic spacer regions, between trnL and trnF, and between trnH and psbA of chloroplast DNA were used. The topologies of trees obtained from ITS and the chloroplast intergenic spacers are largely congruent. S. sonoharae, the representative of the subgenus Symplocos in Asia, was sister to all other species. The position of the American species, S. austromexicana, which also belongs to the subgenus Symplocos, was not well resolved. The phylogenetic tree based on combined sequence data largely supports the monophyletic origin of the infrageneric sections proposed earlier. However, the phylogenetic relationship between them is not well resolved, probably due to rapid diversification. The section Palura, a deciduous group, is well defined in the DNA analysis, suggesting its independent status in the genus Symplocos. In spite of their morphological divergence, the three endemic species of the Bonin Islands are monophyletic. The occurrence of curved seeds seems to be homoplastic, scattered over the phylogenetic tree without showing a particular infrageneric relationship.     

Complete chloroplast genome sequence of a tree fern Alsophila spinulosa : insights into evolutionary changes in fern chloroplast genomes

Background  

Ferns have generally been neglected in studies of chloroplast genomics. Before this study, only one polypod and two basal ferns had their complete chloroplast (cp) genome reported. Tree ferns represent an ancient fern lineage that first occurred in the Late Triassic. In recent phylogenetic analyses, tree ferns were shown to be the sister group of polypods, the most diverse group of living ferns. Availability of cp genome sequence from a tree fern will facilitate interpretation of the evolutionary changes of fern cp genomes. Here we have sequenced the complete cp genome of a scaly tree fern Alsophila spinulosa (Cyatheaceae).     

Molecular phylogeny of sea snakes reveals a rapidly diverged adaptive radiation

Evolutionary relationships within and between the marine hydrophiine sea snake groups have been inferred primarily using morphological characters, and two major groups traditionally are recognized. The Aipysurus group comprises nine species in two genera, and the taxonomically chaotic Hydrophis group comprises as many as 40 species, of which 27 are generally allocated to the genus Hydrophis and 13 to ten additional genera. In addition to these two major groups are three putatively ‘primitive’ monotypic genera, Hydrelaps darwiniensis, Ephalophis greyi and Parahydrophis mertoni. The present study investigated the evolutionary relationships of 23 representative species of marine hydrophiines, comprising 15 species from the Hydrophis group, six species from the Aipysurus group, and H. darwiniensis and P. mertoni, to address two broad aims. First, the aim was to provide a robust phylogeny for sea snakes to test previous phylogenetic hypotheses based on morphology, and thus provide some taxonomic stability to the group. Second, there was interest in evaluating the hypothesis that the Hydrophis group might represent a rapidly diverged adaptive radiation. A large mitochondrial DNA data set based on the cytochrome b gene (1080 bp, 401 parsimony informative) and the 16S rRNA gene (510 bp, 57 parsimony informative) was assembled and these data were analysed using parsimony, maximum‐likelihood and Bayesian approaches. All analyses yielded virtually the same optimal tree, confirming that hydrophiine sea snakes comprise at least three lineages. The Aipysurus group formed a strongly supported and well‐resolved monophyletic clade. The Hydrophis group also formed a strongly supported clade; however, resolution among the genera and species was very poor. Hydrelaps darwiniensis and P. mertoni formed a sister clade to the Hydrophis lineage. Our phylogeny was used to test the validity of previous taxonomic and phylogenetic hypotheses, and to demonstrate that the genus Hydrophis is not monophyletic. Genetic diversity relative to phenotypic diversity is four to seven times greater in the Hydrophis lineage compared with the Aipysurus lineage. The topology of our phylogenetic hypothesis, combined with the levels of genetic divergence relative to morphological diversity, demonstrate that the Hydrophis lineage represents a rapidly diverged adaptive radiation. The data are consistent with the hypothesis that this adaptive radiation may be due to historical sea level fluctuations that have isolated populations and promoted speciation. © 2006 The Linnean Society of London, Biological Journal of the Linnean Society, 2006, 89 , 523–539.     

Monophyly of the family Desmoscolecidae (Nematoda,Demoscolecida) and Its Phylogenetic position inferred from 18S rDNA sequences

To infer the monophyletic origin and phylogenetic relationships of the order Desmoscolecida, a unique and puzzling group of mainly free-living marine nematodes, we newly determined nearly complete 18S rDNA sequences for six marine desmoscolecid nematodes belonging to four genera (Desmoscolex, Greeffiella, Tricoma and Paratricoma). Based on the present data and those of 72 nematode species previously reported, the first molecular phylogenetic analysis focusing on Desmoscolecida was done by using neighbor joining (NJ), maximum parsimony (MP), maximum likelihood (ML) and Bayesian inference (BI) methods. All four resultant trees consistently and strongly supported that the family Desmoscolecidae forms a monophyletic group with very high node confidence values. The monophyletic clade of desmocolecid nematodes was placed as a sister group of the clade including some members of Monhysterida and Araeolaimida, Cyartonema elegans (Cyartonematidae) and Terschellingia longicaudata (Linhomoeidae) in all the analyses. However, the present phylogenetic trees do not show any direct attraction between the families Desmoscolecidae and Cyartonematidae. Within the monophyletic clade of the family Desmoscolecidae in all of the present phylogenetic trees, there were consistently observed two distinct sub-groups which correspond to the subfamilies Desmoscolecinae [Greeffiella sp. + Desmoscolex sp.] and Tricominae [Paratricoma sp. + Tricoma sp].     

Molecular Phylogeny of Some European Heteronemertean (Nemertea) Species and the Monophyletic Status ofRiseriellus, Lineus,andMicrura

The 16S rRNA mitochondrial gene was used to reconstruct the relationships among 10 heteronemertean species (subclass Heteronemertea, phylum Nemertea);Lineus ruberandL. viridisare represented by more than one specimen to assess intraspecific variation in these enigmatic species, and the analysis includes in total 14 terminal taxa incorporating one palaeonemertean species (Tubulanus annulatus) for outgroup rooting. The aligned sequences were subjected to maximum parsimony, maximum-likelihood, and neighbor-joining analyses to estimate the phylogenetic relationship of the species. The results were concordant from all analyses and indicate that neitherLineusnorMicruraare monophyletic taxa, and that there is no support from a phylogenetic point of view to establish the monotypic genusRiseriellus.     

Exogenous double-stranded RNA inhibits the infection physiology of rust fungi to reduce symptoms in planta

Rust fungi (Pucciniales) are a diverse group of plant pathogens in natural and agricultural systems. They pose ongoing threats to the diversity of native flora and cause annual crop yield losses. Agricultural rusts are predominantly managed with fungicides and breeding for resistance, but new control strategies are needed on non-agricultural plants and in fragile ecosystems. RNA interference (RNAi) induced by exogenous double-stranded RNA (dsRNA) has promise as a sustainable approach for managing plant-pathogenic fungi, including rust fungi. We investigated the mechanisms and impact of exogenous dsRNA on rust fungi through in vitro and whole-plant assays using two species as models, Austropuccinia psidii (the cause of myrtle rust) and Coleosporium plumeriae (the cause of frangipani rust). In vitro, dsRNA either associates externally or is internalized by urediniospores during the early stages of germination. The impact of dsRNA on rust infection architecture was examined on artificial leaf surfaces. dsRNA targeting predicted essential genes significantly reduced germination and inhibited development of infection structures, namely appressoria and penetration pegs. Exogenous dsRNA sprayed onto 1-year-old trees significantly reduced myrtle rust symptoms. Furthermore, we used comparative genomics to assess the wide-scale amenability of dsRNA to control rust fungi. We sequenced genomes of six species of rust fungi, including three new families (Araucariomyceaceae, Phragmidiaceae, and Skierkaceae) and identified key genes of the RNAi pathway across 15 species in eight families of Pucciniales. Together, these findings indicate that dsRNA targeting essential genes has potential for broad-use management of rust fungi across natural and agricultural systems.     

Ribosomal DNA-ITS sequence polymorphism in the sugarcane rust,Puccinia kuehnii

The two highly divergent ITS types previously observed in isolates ofPuccinia kuehnii were amplified from the same isolates through the use of ITS type-specific primers for PCR and are therefore considered as polymorphisms of ITS regions within the species. Although homology of sequences of one of the ITS types with otherPuccinia species was of expected levels, significantly high homology of sequences of the other type with those ofCronartium members indicates that abnormal genetic events led to the occurrence of these polymorphic regions. These results indicate that ITS gene tree phylogeny may not reflect true species phylogeny in this group of rust fungi. Rather, D1/D2 region tree phylogeny, which was concordant with the differences in morphology with and among related rusts, more correctly reflects phylogenetic relationships of sugarcane and related grass rusts. contribution No. 159, Laboratory of Plant Parasitic Mycology, Institute of Agriculture and Forestry, University of Tsukuba.     

Allozyme diversity and the evolution ofSymplocos (Symplocaceae) on the Bonin (Ogasawara) Islands

To study the origin and speciation of plants in oceanic islands, electrophoretic analyses have been done on three endemic species ofSymplocos in the Bonin Islands as well as on three other species;S. kuroki, S. nakaharae andS. tanakae which are considered to be closely related to the Bonin endemics. There occur three species:S. kawakamii, S. pergracilis andS. boninensis in Bonin. The genusSymplocos is one which is considered to be diversified in the Bonin Islands. Seven enzyme systems presumed to be encoded by 18 loci were examined. The genetic diversity was low in the island species, as reported in some oceanic island plants of Hawaii and the Bonin Islands. The three endemics share high genetic identities and they clustered together in the tree drawn by the UPGMA method, suggesting that they are a monophyletic group, that is, they result from a single introduction.     

The blood alga: phylogeny of Haematococcus (Chlorophyceae) inferred from ribosomal RNA gene sequence data

The status of the green algal genera Haematococcus and Stephanosphaera has been a source of debate among algal systematists. A phylogenetic alliance between Haematococcus (sensu lato) and the colonial Stephanosphaera was affirmed by earlier molecular phylogenetic investigations. Although the data suggested that the genus Haematococcus may not be a monophyletic group, taxon sampling limited the scope of any potential taxonomic revision. Results from new molecular phylogenetic analyses of data from the 18S and 26S rRNA genes support the establishment of a separate genus, Balticola, as originally proposed by Droop in 1956. Haematococcus remains as a valid genus, with H. pluvialis as its only member. The monotypic status of H. pluvialis is supported both by molecular phylogenetic analyses of the ribosomal RNA genes and assessments of molecular evolution in the ITS2 sequences of H. pluvialis strains. The near-complete absence of compensatory base changes in a sequence-structure analysis of the highly variable ITS2 gene from more than 40 geographically diverse isolates of H. pluvialis corroborates the unity of the species inferred from molecular phylogenetic analyses of 18S and 26S rRNA gene sequence data.     

Phylogenetic Relationships of African Killifishes in the GeneraAphyosemionandFundulopanchaxInferred from Mitochondrial DNA Sequences

We have analyzed the phylogenetic relationships of 52 species representing all defined species groups (J. J. Scheel, 1990, Atlas of Killifishes of the Old World, 448 pp.) of the African aplocheiloid fish generaAphyosemionandFundulopanchaxin order to examine their interrelationships and to reveal trends of karyotypic evolution. The data set comprised 785 total nucleotides from the mitochondrial 12S rRNA and cytochromebgenes. The molecular-based topologies analyzed by both maximum parsimony and neighbor-joining support the monophyly of most previously defined species groups within these two killifish genera. The genusAphyosemionis monophyletic except for the nested position ofFundulopanchax kunzi(batesigroup; subgenusRaddaella) within this clade, suggesting that this taxon was improperly assigned toFundulopanchax.The remainingFundulopanchaxspecies sampled were supported as being monophyletic in most analyses. Relationships among the species groups in both genera were not as strongly supported, suggesting that further data will be required to resolve these relationships. Additional sampling from the 16S rRNA gene allowed further resolution of relationships withinFundulopanchax,more specifically identifying the nonannualscheeligroup as the basal lineage of this otherwise annual genus. Chromosomal evolution withinAphyosemionhas been episodic, with the evolution of a reducedn= 9–10 metacentric complement having occurred in multiple, independent lineages. Polarity of chromosomal reductions within theelegansspecies group appears to support previous hypotheses concerning mechanisms of karyotypic change within the genusAphyosemion.     

Toward resolving family-level relationships in rust fungi (Uredinales)

Rust fungi (Basidiomycota, Uredinales) consist of more than 7000 species of obligate plant pathogens that possess some of the most complex life cycles in the Eumycota. Traditionally, a limited number of synapomorphic characters and incomplete life-cycle and host-specificity data have hampered phylogenetic inference within the Uredinales. The application of modern molecular characters to rust systematics has been limited, and current contradictions, especially in the deeper nodes, have not yet been resolved. In this study, two nuclear rDNA genes (18S and 28S) were examined across the breadth of the Uredinales to resolve some systematic conflicts and provide a framework for further studies of the group. Three suborders of rusts are recovered. Of the 13 rust families most widely accepted, 8 are supported in full or in part (Coleosporiaceae, Melampsoraceae, Mikronegeriaceae, Phakopsoraceae p.p., Phragmidiaceae, Pileolariaceae, Pucciniaceae, Raveneliaceae), 3 are redundant (Cronartiaceae, Pucciniastraceae, Pucciniosiraceae), and the status of 2 (Chaconiaceae, Uropyxidaceae) could not be resolved. The Mikronegeriaceae and Caeoma torreyae are the most basal rusts sampled. It is concluded that morphology alone is a poor predictor of rust relationships at most levels. Host selection, on the other hand, has played a significant role in rust evolution. Mention of trade names or commercial products in this publication is solely for the purpose of providing specific information and does not imply recommendation or endorsement by the US Department of Agriculture.     

Green Rust Formation from the Bioreduction of γ –FeOOH (Lepidocrocite): Comparison of Several Shewanella Species

Green rusts are mixed ferrous/ferric hydroxides that typically form under weakly acidic to alkaline conditions in suboxic environments. The recent identification of green rusts as products of the reduction of Fe(III) oxides and oxyhydroxides by Shewanella putrefaciens, a dissimilatory iron-reducing bacterium (DIRB), suggests that green rusts may play a role in the redox cycling of Fe in many aquatic and terrestrial environments. We examined the potential for green rust formation resulting from the bioreduction of lepidocrocite(γ -FeOOH) by a series of Shewanella species (S. alga BrY, S. amazonensis SB2B, S. baltica OS155, S. denitrificans OS217T, S. loihica PV-4, S. oneidensis MR-1, S. putrefaciens ATCC 8071, S. putrefaciens CN32, S. saccharophilia, and Shewanella sp. ANA-3). All Shewanella species, with the exception of S. denitrificans OS217T, were able to couple the oxidation of formate to the reduction of Fe(III) in lepidocrocite; however there were significant differences among species with respect to the rate and extent of Fe(II) production. Despite these differences, green rust was the only Fe(II)-bearing solid phase formed under our experimental conditions, as indicated by X-ray diffraction, Mössbauer spectroscopy, and scanning electron microscopy. The formation of green rust by Shewanella species isolated from a wide range of habitats and possessing varied metabolic capabilities suggests that under favorable conditions biogenic green rusts may be formed by a diverse array of DIRB.     

Phylogenetic species recognition reveals host-specific lineages among poplar rust fungi

Fungal species belonging to the genus Melampsora (Basidiomycota, Pucciniales) comprise rust pathogens that alternate between Salicaceae and other plant hosts. Species delineation and identification are difficult within this group due to the paucity of observable morphological features. Several Melampsora rusts are highly host-specific and this feature has been used for identification at the species level. However, this criterion is not always reliable since different Melampsora rust species can overlap on one host but specialize on a different one. To date, two different species recognition methods are used to recognize and define species within the Melampsora genus: (i) morphological species recognition, which is based solely on morphological criteria; and (ii) ecological species recognition, which combines morphological criteria with host range to recognize and define species. In order to clarify species recognition within the Melampsora genus, we applied phylogenetic species recognition to Melampsora poplar rusts by conducting molecular phylogenetic analyses on 15 Melampsora taxa using six nuclear and mitochondrial loci. By assessing the genealogical concordance between phylogenies, we identified 12 lineages that evolved independently, corresponding to distinct phylogenetic species. All 12 lineages were concordant with host specialization, but only three belonged to strictly defined morphological species. The estimation of the species tree obtained with Bayesian concordance analysis highlighted a potential co-evolutionary history between Melampsora species and their reciprocal aecial host plants. Within the Melampsora speciation process, aecial host may have had a strong effect on ancestral evolution, whereas telial host specificity seems to have evolved more recently. The morphological characters initially used to define species boundaries in the Melampsora genus are not reflective of the evolutionary and genetic relationships among poplar rusts. In order to construct a more meaningful taxonomy, host specificity must be considered an important criterion for delineating and describing species within the genus Melampsora as previously suggested by ecological species recognition.     

Phylogenetic relationships of Cyprinidae (Teleostei: Cypriniformes) inferred from the partial <Emphasis Type="Italic">S6K1</Emphasis> gene sequences and implication of indel sites in intron 1

The family Cyprinidae is widely distributed in East Asia, and has the important phylogenetic significance in the fish evolution. In this study, the 5′ end partial sequences (containing exon 1, exon 2 and indel 1) of S6K1 gene were obtained from 30 representative species in Cyprinidae and outgroup using PCR amplification and sequencing. The phylogenetic relationships of Cyprinidae were reconstructed with neighbor joining (NJ), maximum parsimony (MP), maximum likelihood (ML), and Bayesian methods. Myxocyprinus asiaticus (Catostomidae) was assigned to the outgroup taxon. Similar phylogenetic relationships within the family Cyprinidae were achieved with the four analyses. Leuciscini and Barbini were monophyletic lineages respectively with the high nodal supports. Leuciscini comprises Hypophthalmichthyinae, Xenocyprinae, Cultrinae, Gobioninae, Acheilognathinae and East Asian species of Leuciscinae and Danioninae. Monophyly of East Asian clade was supported with high nodal support. Barbini comprises Schizothoracinae, Barbinae, Cyprininae and Labeoninae. The monophyletic lineage consisting of Danio rerio, D. myersi, and Rasbora trilineata was basal in the tree. In addition, the large fragment indels in intron 1 were analyzed to improve the understanding of Cyprinidae relationships. The results showed that the large fragment indels were correlated with the relations among species. Some conserved regions in intron 1 were thought to be involved in the functional regulation. However, no correlation was found between sequence variations and species characteristic size.     

Evolution of green plants and their relationship with other photosynthetic eukaryotes as deduced from 5S ribosomal RNA sequences

The nucleotide sequence of cytoplasmic 5S ribosomal RNAs from three gymnosperms,Pinus contorta, Taxus baccata andJuniperus media and from one fern,Pteridium aquilinum, have been determined. These sequences were aligned with all hitherto known cytoplasmic 5S ribosomal RNA sequences of photosynthetic eukaryotes. A dendrogram based on that set of sequences was constructed by a distance matrix method and the resulting tree compared with established views concerning plant and algal evolution. The following monophyletic groups of photosynthetic eukaryotes are recognizable: theRhodophyta, a group consisting ofPhaeophyta, Bacillariophyta andChrysophyta, and the green plants, the latter comprising green algae,Bryophyta, Pteridophyta andSpermatophyta. According to our 5S ribosomal RNA tree, green plants may have originated from some type of a green flagellated organism such asChlamydomonas. The land plants seem to have originated from some form of charophyte such asNitella. 5S ribosomal RNA seems to be less appropriate to estimate dissimilarities between species which have diverged relatively recently, like the angiosperms. Therefore, a precise evolutionary process is difficult to reconstruct for members of this group.