Expansion of the IR in the chloroplast genomes of buckwheat species is due to incorporation of an SSC sequence that could be mediated by an inversion

Phylogenomics and plastome evolution of Indigofera (Fabaceae)

Introduction

Indigofera L. is the third largest genus in Fabaceae and includes economically important species that are used for indigo dye-producing, medicinal, ornamental, and soil and water conservation. The genus is taxonomically difficult due to the high level of overlap in morphological characters of interspecies, fewer reliability states for classification, and extensive adaptive evolution. Previous characteristic-based taxonomy and nuclear ITS-based phylogenies have contributed to our understanding of Indigofera taxonomy and evolution. However, the lack of chloroplast genomic resources limits our comprehensive understanding of the phylogenetic relationships and evolutionary processes of Indigofera.

Methods

Here, we newly assembled 18 chloroplast genomes of Indigofera. We performed a series of analyses of genome structure, nucleotide diversity, phylogenetic analysis, species pairwise Ka/Ks ratios, and positive selection analysis by combining with allied species in Papilionoideae.

Results and discussion

The chloroplast genomes of Indigofera exhibited highly conserved structures and ranged in size from 157,918 to 160,040 bp, containing 83 protein-coding genes, 37 tRNA genes, and eight rRNA genes. Thirteen highly variable regions were identified, of which trnK-rbcL, ndhF-trnL, and ycf1 were considered as candidate DNA barcodes for species identification of Indigofera. Phylogenetic analysis using maximum likelihood (ML) and Bayesian inference (BI) methods based on complete chloroplast genome and protein-coding genes (PCGs) generated a well-resolved phylogeny of Indigofera and allied species. Indigofera monophyly was strongly supported, and four monophyletic lineages (i.e., the Pantropical, East Asian, Tethyan, and Palaeotropical clades) were resolved within the genus. The species pairwise Ka/Ks ratios showed values lower than 1, and 13 genes with significant posterior probabilities for codon sites were identified in the positive selection analysis using the branch-site model, eight of which were associated with photosynthesis. Positive selection of accD suggested that Indigofera species have experienced adaptive evolution to selection pressures imposed by their herbivores and pathogens. Our study provided insight into the structural variation of chloroplast genomes, phylogenetic relationships, and adaptive evolution in Indigofera. These results will facilitate future studies on species identification, interspecific and intraspecific delimitation, adaptive evolution, and the phylogenetic relationships of the genus Indigofera.

Comparative chloroplast genome analysis of medicinally important Veratrum (Melanthiaceae) in China: Insights into genomic characterization and phylogenetic relationships

Members of Veratrum are perennial herbs widely used in traditional Chinese medicine to induce vomiting, resolve blood stasis and relieve pain. However, the intrageneric classification and phylogenetic relationships within Veratrum have long been controversial due to the complexity of morphological variations and lack of high-resolution molecular markers. In this study, we reevaluated the infrageneric relationships with the genus Veratrum using complete chloroplast genome sequence data. Herein, the complete cp genomes of ten species of Veratrum were newly sequenced and characterized. The complete cp genomes of ten species of Veratrum had the typical quadripartite structure, ranging from 151,597 bp to 153,711 bp in size and comprising a total of 135 genes. The structure of Veratrum cp genomes (i.e., gene order, content, and genome components) was highly similar across species. The number of simple sequence repeats (SSRs) ranged from 63 to 78, and of long repeats ranged from 31 to 35. Eight highly divergent regions (ndhF, psbC-psbZ, psbK-psbI, rpoB-trnC_GCA, trnK_UUU-trnQ_UUG, trnS_GCU-trnG_UCC, trnT_UGU-trnL_UAA and ycf1) were identified and are potentially useful for the DNA barcoding of Veratrum. Phylogenetic analysis among 29 taxa based on cp genomes, total genes, protein-coding genes and intergenic regions strongly supported the monophyly of Veratrum. The circumscription and relationships of the infrageneric taxa of Veratrum were well-presented with great resolution. These results will facilitate the identification, taxonomy, and utilization of Veratrum plants as well as the evolutionary studies of Melanthiaceae.

Comparative plastomics of Amaryllidaceae: inverted repeat expansion and the degradation of the ndh genes in Strumaria truncata Jacq

Amaryllidaceae is a widespread and distinctive plant family contributing both food and ornamental plants. Here we present an initial survey of plastomes across the family and report on both structural rearrangements and gene losses. Most plastomes in the family are of similar gene arrangement and content however some taxa have shown gains in plastome length while in several taxa there is evidence of gene loss. Strumaria truncata shows a substantial loss of ndh family genes while three other taxa show loss of cemA, which has been reported only rarely. Our sparse sampling of the family has detected sufficient variation to suggest further sampling across the family could be a rich source of new information on plastome variation and evolution.

Comparative Plastomes and Phylogenetic Analysis of Cleistogenes and Closely Related Genera (Poaceae)

Cleistogenes (Orininae, Cynodonteae, Chloridoideae, Poaceae) is an ecologically important genus. The phylogenetic placement of Cleistogenes and phylogenetic relationships among Cleistogenes taxa remain controversial for a long time. To resolve the intra- and inter-generic relationships of Cleistogenes, the plastomes of 12 Cleistogenes taxa (including 8 species and 4 varieties), one Orinus species, 15 Triodia species, two Tripogon species, and two Aeluropus species were included in the present study. All the taxa showed a similar pattern in plastome structure, gene order, gene content, and IR boundaries. The number of simple sequence repeats ranged from 145 (O. kokonorica) to 161 (T. plurinervata and T. schinzii). Moreover, 1,687 repeats were identified in these taxa, including 1,012 forward, 650 palindromic, 24 reverse, and one complement. Codon usage analysis revealed that these plastomes contained 16,633 (T. stipoides) to 16,678 (T. tomentosa) codons. Sequence divergence analysis among Cleistogenes and closely related genera identified five non-coding regions (trnS-UGA-psbZ, rpl32-trnL-UAG, trnQ-UUG-psbK, trnD-GUC-psbM, trnT-GGU-trnE-UUC). Phylogenetic analysis of complete plastomes indicated that Cleistogenes is sister to a clade composed of Orinus and Triodia, whereas it did not support the sister relationship between the recently proposed subtribe Orininae (Cleistogenes and Orinus) and Triodia. The subtribe Orininae was not supported by our complete plastome data. The split between Cleistogenes and Orinus-Triodia clade go back to 14.01 Ma. Besides, our findings suggested that C. squarrosa and C. songorica are the successive early diverging groups in the phylogenetic analysis. The other 10 taxa are divided into two groups: a monophyletic group composed of Cleistogenes sp. nov. and C. caespitosa var. ramosa is sister to other eight Cleistogenes taxa. Cleistogenes was estimated to have experienced rapid divergence within a short period, which could be a major obstacle in resolving phylogenetic relationships within Cleistogenes. Collectively, our results provided valuable insights into the phylogenetic study of grass species.

Complete Plastid Genome Sequencing of Eight Species from Hansenia, Haplosphaera and Sinodielsia (Apiaceae): Comparative Analyses and Phylogenetic Implications

Hansenia Turcz., Haplosphaera Hand.-Mazz. and Sinodielsia H.Wolff are three Apiaceae genera endemic to the Hengduan Mountains and the Himalayas, which usually inhabit elevations greater than 2000 m. The phylogenetic relationships between and within the genera were uncertain, especially the placement of Hap. himalayensis and S. microloba. Therefore, we aimed to conduct comparative (simple sequence repeat (SSR) structure, codon usage bias, nucleotide diversity (Pi) and inverted repeat (IR) boundaries) and phylogenetic analyses of Hansenia, Haplosphaera and Sinodielsia (also compared with Chamaesium and Bupleurum) to reduce uncertainties in intergeneric and interspecific relationships. We newly assembled eight plastid genomes from Hansenia, Haplosphaera and Sinodielsia species, and analyzed them with two plastid genomes from GenBank of Hap. phaea,S. yunnanensis. Phylogenetic analyses used these ten genomes and another 22 plastid genome sequences of Apiaceae. We found that the newly assembled eight genomes ranged from 155,435 bp to 157,797 bp in length and all had a typical quadripartite structure. Fifty-five to 75 SSRs were found in Hansenia, Haplosphaera and Sinodielsia species, and the most abundant SSR was mononucleotide, which accounted for 58.47% of Hansenia, 60.21% of Haplosphaera and 48.01% of Sinodielsia. There was no evident divergence of codon usage frequency between the three genera, where codons ranged from 21,134 to 21,254. The Pi analysis showed that trnE(UUC)-trnT(GGU), trnH(GUG)-psbA and trnE(UUC)-trnT(GGU) spacer regions had the highest Pi values in the plastid genomes of Hansenia (0.01889), Haplosphaera (0.04333) and Sinodielsia (0.01222), respectively. The ndhG-ndhI spacer regions were found in all three genera to have higher diversity values (Pi values: 0.01028-0.2), and thus may provide potential DNA barcodes in phylogenetic analysis. IR boundary analysis showed that the length of rps19 and ycf1 genes entering IRs were usually stable in the same genus. Our phylogenetic tree demonstrated that Hap. himalayensis is sister to Han. weberbaueriana; meanwhile, Haplosphaera and Hansenia are nested together in the East Asia clade, and S. microloba is nested within individuals of S. yunnanensis in the Acronema clade. This study will enrich the complete plastid genome dataset of the Apiaceae genera and has provided a new insight into phylogeny reconstruction using complete plastid genomes of Hansenia, Haplosphaera and Sinodielsia.

Comparative analysis of four Zantedeschia chloroplast genomes: expansion and contraction of the IR region, phylogenetic analyses and SSR genetic diversity assessment

The horticulturally important genus Zantedeschia (Araceae) comprises eight species of herbaceous perennials. We sequenced, assembled and analyzed the chloroplast (cp) genomes of four species of Zantedeschia (Z. aethiopica, Z. odorata, Z. elliottiana, and Z. rehmannii) to investigate the structure of the cp genome in the genus. According to our results, the cp genome of Zantedeschia ranges in size from 169,065 bp (Z. aethiopica) to 175,906 bp (Z. elliottiana). We identified a total of 112 unique genes, including 78 protein-coding genes, 30 transfer RNA (tRNA) genes and four ribosomal RNA (rRNA) genes. Comparison of our results with cp genomes from other species in the Araceae suggests that the relatively large sizes of the Zantedeschia cp genomes may result from inverted repeats (IR) region expansion. The sampled Zantedeschia species formed a monophylogenetic clade in our phylogenetic analysis. Furthermore, the long single copy (LSC) and short single copy (SSC) regions in Zantedeschia are more divergent than the IR regions in the same genus, and non-coding regions showed generally higher divergence than coding regions. We identified a total of 410 cpSSR sites from the four Zantedeschia species studied. Genetic diversity analyses based on four polymorphic SSR markers from 134 cultivars of Zantedeschia suggested that high genetic diversity (I = 0.934; Ne = 2.371) is present in the Zantedeschia cultivars. High genetic polymorphism from the cpSSR region suggests that cpSSR could be an effective tool for genetic diversity assessment and identification of Zantedeschia varieties.

Comparative analysis of the complete chloroplast genome sequences of six species of Pulsatilla Miller, Ranunculaceae

BACKGROUND

Baitouweng is a traditional Chinese medicine with a long history of different applications. Although referred to as a single medicine, Baitouweng is actually comprised of many closely related species. It is therefore critically important to identify the different species that are utilized in these medicinal applications. Knowledge about their phylogenetic relationships can be derived from their chloroplast genomes and may provide additional insights into development of molecular markers.

METHODS

Genomic DNA was extracted from six species of Pulsatilla and then sequenced on an Illumina HiSeq 4000. Sequences were assembled into contigs by SOAPdenovo 2.04, aligned to the reference genome using BLAST, and then manually corrected. Genome annotation was performed by the online DOGMA tool. General characteristics of the cp genomes of the six species were analyzed and compared with closely related species. Additionally, phylogenetic trees were constructed, based on single nucleotide polymorphisms (SNPs) and 51 shared protein-coding gene sequences in the cp genome among all 31 species via maximum likelihood.

RESULTS

The size of cp genomes of P. chinensis (Bge.) Regel, P. chinensis (Bge.) Regel var. kissii (Mandl) S. H. Li et Y. H. Huang, P. cernua (Thunb.) Bercht. et Opiz f. plumbea J. X. Ji et Y. T. zhao, P. dahurica (Fisch.) Spreng, P. turczaninovii Kryl. et Serg, and P. cernua (Thunb.) Bercht. et Opiz. were 163,851 bp, 163,756 bp, 162,481 bp, 162,450 bp, 162,795 bp, and 162,924 bp, respectively. Each species included two inverted repeat regions, a small single-copy region, and a large single-copy region. A total of 134 genes were annotated, including 90 protein-coding genes, 36 tRNAs, and eight rRNAs across all species. In simple sequence repeat analysis, only P. dahurica was found to contain hexanucleotide repeats. A total of 26, 39, 32, 37, 32 and 43 large repeat sequences were identified in the genic regions of the six Pulsatilla species. Nucleotide diversity analysis revealed that the rpl36 gene and ccsA-ndhD region have the highest Pi value. In addition, two phylogenetic trees of the cp genomes were constructed, which laced all Pulsatilla species into one branch within Ranunculaceae.

CONCLUSIONS

We identified and analyzed the cp genome features of six species of P. Miller, with implications for species identification and phylogenetic analysis.

Total duplication of the small single copy region in the angiosperm plastome: Rearrangement and inverted repeat instability in Asarum

PREMISE OF THE STUDY

As more plastomes are assembled, it is evident that rearrangements, losses, intergenic spacer expansion and contraction, and syntenic breaks within otherwise functioning plastids are more common than was thought previously, and such changes have developed independently in disparate lineages. However, to date, the magnoliids remain characterized by their highly conserved plastid genomes (plastomes).

METHODS

Illumina HiSeq and MiSeq platforms were used to sequence the plastomes of Saruma henryi and those of representative species from each of the six taxonomic sections of Asarum. Sequenced plastomes were compared in a phylogenetic context provided by maximum likelihood and parsimony inferences made using an additional 18 publicly available plastomes from early-diverging angiosperm lineages.

KEY RESULTS

In contrast to previously published magnoliid plastomes and the newly sequenced Saruma henryi plastome published here, Asarum plastomes have undergone extensive disruption and contain extremely lengthy AT-repeat regions. The entirety of the small single copy region (SSC) of A. canadense and A. sieboldii var. sieboldii has been incorporated into the inverted repeat regions (IR), and the SSC of A. delavayi is only 14 bp long. All sampled Asarum plastomes share an inversion of a large portion of the large single copy region (LSC) such that trnE-UUC is adjacent to the LSC-IR boundary.

CONCLUSIONS

Plastome divergence in Asarum appears to be consistent with trends seen in highly rearranged plastomes of the monocots and eudicots. We propose that plastome instability in Asarum is due to repetitive motifs that serve as recombinatory substrates and reduce genome stability.

Comparative genomics of four Liliales families inferred from the complete chloroplast genome sequence of Veratrum patulum O. Loes. (Melanthiaceae)

The sequence of the chloroplast genome, which is inherited maternally, contains useful information for many scientific fields such as plant systematics, biogeography and biotechnology because its characteristics are highly conserved among species. There is an increase in chloroplast genomes of angiosperms that have been sequenced in recent years. In this study, the nucleotide sequence of the chloroplast genome (cpDNA) of Veratrum patulum Loes. (Melanthiaceae, Liliales) was analyzed completely. The circular double-stranded DNA of 153,699 bp consists of two inverted repeat (IR) regions of 26,360 bp each, a large single copy of 83,372 bp, and a small single copy of 17,607 bp. This plastome contains 81 protein-coding genes, 30 distinct tRNA and four genes of rRNA. In addition, there are six hypothetical coding regions (ycf1, ycf2, ycf3, ycf4, ycf15 and ycf68) and two open reading frames (ORF42 and ORF56), which are also found in the chloroplast genomes of the other species. The gene orders and gene contents of the V. patulum plastid genome are similar to that of Smilax china, Lilium longiflorum and Alstroemeria aurea, members of the Smilacaceae, Liliaceae and Alstroemeriaceae (Liliales), respectively. However, the loss rps16 exon 2 in V. patulum results in the difference in the large single copy regions in comparison with other species. The base substitution rate is quite similar among genes of these species. Additionally, the base substitution rate of inverted repeat region was smaller than that of single copy regions in all observed species of Liliales. The IR regions were expanded to trnH_GUG in V. patulum, a part of rps19 in L. longiflorum and A. aurea, and whole sequence of rps19 in S. china. Furthermore, the IGS lengths of rbcL-accD-psaI region were variable among Liliales species, suggesting that this region might be a hotspot of indel events and the informative site for phylogenetic studies in Liliales. In general, the whole chloroplast genome of V. patulum, a potential medicinal plant, will contribute to research on the genetic applications of this genus.

Migration of endpoints of two genes relative to boundaries between regions of the plastid genome in the grass family (Poaceae)

Overlapping genes occur widely in microorganisms and in some plastid genomes, but unique properties are observed when such genes span the boundaries between single-copy and repeat regions. The termini of ndhH and ndhF, situated near opposite ends of the small single-copy region (SSC) in the plastid genomes of grasses (Poaceae), have migrated repeatedly into and out of the adjacent inverted-repeat regions (IR). The two genes are transcribed in the same direction, and the 5' terminus of ndhH extends into the IR in some species, while the 3' terminus of ndhF extends into the IR in others. When both genes extend into the IR, portions of the genes overlap and are encoded by the same nucleotide positions. Fine-scale mapping of the SSC-IR junctions across a sample of 92 grasses and outgroups, integrated into a phylogenetic analysis, indicates that the earliest grasses resembled the related taxa Joinvillea (Joinvilleaceae) and Ecdeiocolea (Ecdeiocoleaceae), with ca. 180 nucleotides of ndhH extending into the IR, and with ndhF confined to the SSC. This structure is maintained in early-diverging grass lineages and in most species of the BEP clade. In the PACMAD clade, ndhH lies completely or nearly completely within the SSC, and ca. 20 nucleotides of ndhF extend into the IR. The nucleotide substitution rate has increased in the PACMAD clade in the portion of ndhH that has migrated into the SSC.

Implications of the plastid genome sequence of typha (typhaceae, poales) for understanding genome evolution in poaceae

Plastid genomes of the grasses (Poaceae) are unusual in their organization and rates of sequence evolution. There has been a recent surge in the availability of grass plastid genome sequences, but a comprehensive comparative analysis of genome evolution has not been performed that includes any related families in the Poales. We report on the plastid genome of Typha latifolia, the first non-grass Poales sequenced to date, and we present comparisons of genome organization and sequence evolution within Poales. Our results confirm that grass plastid genomes exhibit acceleration in both genomic rearrangements and nucleotide substitutions. Poaceae have multiple structural rearrangements, including three inversions, three genes losses (accD, ycf1, ycf2), intron losses in two genes (clpP, rpoC1), and expansion of the inverted repeat (IR) into both large and small single-copy regions. These rearrangements are restricted to the Poaceae, and IR expansion into the small single-copy region correlates with the phylogeny of the family. Comparisons of 73 protein-coding genes for 47 angiosperms including nine Poaceae genera confirm that the branch leading to Poaceae has significantly accelerated rates of change relative to other monocots and angiosperms. Furthermore, rates of sequence evolution within grasses are lower, indicating a deceleration during diversification of the family. Overall there is a strong correlation between accelerated rates of genomic rearrangements and nucleotide substitutions in Poaceae, a phenomenon that has been noted recently throughout angiosperms. The cause of the correlation is unknown, but faulty DNA repair has been suggested in other systems including bacterial and animal mitochondrial genomes.

Comparative chloroplast genomics and phylogenetics of Fagopyrum esculentum ssp. ancestrale -a wild ancestor of cultivated buckwheat

BACKGROUND

Chloroplast genome sequences are extremely informative about species-interrelationships owing to its non-meiotic and often uniparental inheritance over generations. The subject of our study, Fagopyrum esculentum, is a member of the family Polygonaceae belonging to the order Caryophyllales. An uncertainty remains regarding the affinity of Caryophyllales and the asterids that could be due to undersampling of the taxa. With that background, having access to the complete chloroplast genome sequence for Fagopyrum becomes quite pertinent.

RESULTS

We report the complete chloroplast genome sequence of a wild ancestor of cultivated buckwheat, Fagopyrum esculentum ssp. ancestrale. The sequence was rapidly determined using a previously described approach that utilized a PCR-based method and employed universal primers, designed on the scaffold of multiple sequence alignment of chloroplast genomes. The gene content and order in buckwheat chloroplast genome is similar to Spinacia oleracea. However, some unique structural differences exist: the presence of an intron in the rpl2 gene, a frameshift mutation in the rpl23 gene and extension of the inverted repeat region to include the ycf1 gene. Phylogenetic analysis of 61 protein-coding gene sequences from 44 complete plastid genomes provided strong support for the sister relationships of Caryophyllales (including Polygonaceae) to asterids. Further, our analysis also provided support for Amborella as sister to all other angiosperms, but interestingly, in the bayesian phylogeny inference based on first two codon positions Amborella united with Nymphaeales.

CONCLUSION

Comparative genomics analyses revealed that the Fagopyrum chloroplast genome harbors the characteristic gene content and organization as has been described for several other chloroplast genomes. However, it has some unique structural features distinct from previously reported complete chloroplast genome sequences. Phylogenetic analysis of the dataset, including this new sequence from non-core Caryophyllales supports the sister relationship between Caryophyllales and asterids.

Dynamics and evolution of the inverted repeat-large single copy junctions in the chloroplast genomes of monocots

Background

Various expansions or contractions of inverted repeats (IRs) in chloroplast genomes led to fluxes in the IR-LSC (large single copy) junctions. Previous studies revealed that some monocot IRs contain a trnH-rps19 gene cluster, and it has been speculated that this may be an evidence of a duplication event prior to the divergence of monocot lineages. Therefore, we compared the organizations of genes flanking two IR-LSC junctions in 123 angiosperm representatives to uncover the evolutionary dynamics of IR-LSC junctions in basal angiosperms and monocots.

Results

The organizations of genes flanking IR-LSC junctions in angiosperms can be classified into three types. Generally each IR of monocots contains a trnH-rps19 gene cluster near the IR-LSC junctions, which differs from those in non-monocot angiosperms. Moreover, IRs expanded more progressively in monocots than in non-monocot angiosperms. IR-LSC junctions commonly occurred at polyA tract or A-rich regions in angiosperms. Our RT-PCR assays indicate that in monocot IR_A the trnH-rps19 gene cluster is regulated by two opposing promoters, S10_A and psbA.

Conclusion

Two hypotheses are proposed to account for the evolution of IR expansions in monocots. Based on our observations, the inclusion of a trnH-rps19 cluster in majority of monocot IRs could be reasonably explained by the hypothesis that a DSB event first occurred at IR_B and led to the expansion of IRs to trnH, followed by a successive DSB event within IR_A and lead to the expansion of IRs to rps19 or to rpl22 so far. This implies that the duplication of trnH-rps19 gene cluster was prior to the diversification of extant monocot lineages. The duplicated trnH genes in the IR_B of most monocots and non-monocot angiosperms have distinct fates, which are likely regulated by different expression levels of S10_A and S10_B promoters. Further study is needed to unravel the evolutionary significance of IR expansion in more recently diverged monocots.

Phylogenetic and evolutionary implications of complete chloroplast genome sequences of four early-diverging angiosperms: Buxus (Buxaceae), Chloranthus (Chloranthaceae), Dioscorea (Dioscoreaceae), and Illicium (Schisandraceae)

We have determined the complete chloroplast genome sequences of four early-diverging lineages of angiosperms, Buxus (Buxaceae), Chloranthus (Chloranthaceae), Dioscorea (Dioscoreaceae), and Illicium (Schisandraceae), to examine the organization and evolution of plastid genomes and to estimate phylogenetic relationships among angiosperms. For the most part, the organization of these plastid genomes is quite similar to the ancestral angiosperm plastid genome with a few notable exceptions. Dioscorea has lost one protein-coding gene, rps16; this gene loss has also happened independently in four other land plant lineages, liverworts, conifers, Populus, and legumes. There has also been a small expansion of the inverted repeat (IR) in Dioscorea that has duplicated trnH-GUG. This event has also occurred multiple times in angiosperms, including in monocots, and in the two basal angiosperms Nuphar and Drimys. The Illicium chloroplast genome is unusual by having a 10 kb contraction of the IR. The four taxa sequenced represent key groups in resolving phylogenetic relationships among angiosperms. Illicium is one of the basal angiosperms in the Austrobaileyales, Chloranthus (Chloranthales) remains unplaced in angiosperm classifications, and Buxus and Dioscorea are early-diverging eudicots and monocots, respectively. We have used sequences for 61 shared protein-coding genes from these four genomes and combined them with sequences from 35 other genomes to estimate phylogenetic relationships using parsimony, likelihood, and Bayesian methods. There is strong congruence among the trees generated by the three methods, and most nodes have high levels of support. The results indicate that Amborella alone is sister to the remaining angiosperms; the Nymphaeales represent the next-diverging clade followed by Illicium; Chloranthus is sister to the magnoliids and together this group is sister to a large clade that includes eudicots and monocots; and Dioscorea represents an early-diverging lineage of monocots just internal to Acorus.