Comparative Plastid Genome and Phylogenomic Analyses of Potamogeton Species

Potamogetonaceae are aquatic plants divided into six genera. The largest genus in the family is Potamogeton, which is morphologically diverse with many hybrids and polyploids. Potamogetonaceae plastomes were conserved in genome size (155,863 bp–156,669 bp), gene contents (113 genes in total, comprising 79 protein-coding genes and 30 tRNA and 4 rRNA genes), and GC content (36.5%). However, we detected a duplication of the trnH gene in the IR region of the Potamogeton crispus and P. maakianus plastomes. A comparative analysis of Alismatales indicated that the plastomes of Potamogetonaceae, Cymodaceae, and Ruppiaceae have experienced a 6-kb inversion of the rbcL-trnV region and the ndh complex has been lost in the Najas flexilis plastome. Five divergent hotspots (rps16-trnQ, atpF intron, rpoB-trnC, trnC-psbM, and ndhF-rpl32) were identified among the Potamogeton plastomes, which will be useful for species identification. Phylogenetic analyses showed that the family Potamogetonaceae is a well-defined with 100% bootstrap support and divided into two different clades, Potamogeton and Stuckenia. Compared to the nucleotide substitution rates among Alismatales, we found neutral selection in all plastid genes of Potamogeton species. Our results reveal the complete plastome sequences of Potamogeton species, and will be helpful for taxonomic identification, the elucidation of phylogenetic relationships, and the plastome structural analysis of aquatic plants.


Introduction
Potamogetonaceae is an aquatic family comprising six genera (Althenia, Groenlandia, Lapilaena, Zannichillia, Stuckenia, and Potamogeton) and 110 species [1].Potamogeton L. is used as food and a habitat for aquatic animals [2][3][4][5], and is divided into two subgenera Potamogeton and Coleogetonia [4].However, the subgenus Coleogetonia was previously treated as an independent genus by Haynes [6], and was also treated as a synonym of genus Stuckenia Börner by Holub [7].Potamogeton and Stuckenia differ in leaf shape, peduncle anatomy, and ploidy level [6,7].Potamogeton species have highly similar morphological characteristics, such as leaves, seeds, and pollen, as well as various leaf shapes depending on the growing conditions [8][9][10].Moreover, many Potamogeton species have undergone hybridization and polyploidization [3,[11][12][13][14][15].Hence, Potamogeton species are difficult to delimit taxonomically via morphological characteristics.Kaplan [11] reported that Potamogeton species comprise at least 50 hybrids worldwide.A previous molecular study using a 5S nuclear ribosomal array (5S-NTS) and plastid non-coding regions (psbA-trnH region and trnL intron) showed that Potamogeton was divided into two major groups: broadleaved species and narrow-leaved species [16].However, Iida et al. [17] indicated that the two major groups were not supported by the plastid non-coding region (trnT-L intron), and they proposed two alternative groups based on the shape of the submerged leaves and Genes 2023, 14,1914 2 of 14 the anatomical features of the stem, and on linear submerged leaves and the presence of sub-epidermal bundles [17].In general, the relationships among Potamogeton species are still unclear [16][17][18][19][20].

Plant Materials and DNA Extraction
Fresh leaves of Potamogeton species were sampled from a natural population in South Korea.All voucher specimens were deposited at the Nakdonggang National Institute of Biological Resources (NNIBR).Total genomic DNA was extracted using the DNeasy Plant Mini Kit (Qiagen Inc., Valencia, CA, USA).

Comparative Genomics, Divergence Hotspot and Repeat Analysis
The six completed chloroplast genome sequences were aligned using MAFFT [54].Nucleotide diversity (Pi) was determined using DnaSP v. 6.0 [55].The step size was set to 200 bp and the window length to 600 bp.

Phylogenetic and Substitution Rate Analysis
The plastomes of 20 Alismatales species including six Potamogeton species (two of P. perfoliatus) and one outgroup (Acorus gramineus) were used.The 65 shared-protein coding genes were aligned using MAFFT v.7.222 [54].A maximum likelihood (ML) tree was constructed on Geneious Prime using RAxML v. 8.2.11 [58] and the GTRGAMMA model with 1000 bootstrap replicates.The Bayesian inference (BI) method for phylogenies was implemented with MrBayes [59].Markov chain Monte Carlo (MCMC) analysis was run for one million generations.The trees were sampled every 1000 generations and the initial 25% were discarded as burn-in.The remaining trees were used to build a majority-rule consensus tree.
The dN and dS rates were estimated for each of the 48 shared protein-coding genes (>200 bp) using CODEML in PAML v. 4.8 [60].The phylogenetic tree generated in the previous section was used as the constraint tree for all rate comparisons.Codon frequencies were determined in PAML using the F3 × 4 model, and gapped regions were excluded with the "clean data = 1" parameter option.The transition/transversion ratio and dN/dS values were estimated using the initial values of 2.0 and 0.4, respectively.
previous section was used as the constraint tree for all rate comparisons.Codon frequencies were determined in PAML using the F3 × 4 model, and gapped regions were excluded with the "clean data = 1" parameter option.The transition/transversion ratio and dN/dS values were estimated using the initial values of 2.0 and 0.4, respectively.

Genome Features of Potamogetonaceae Species
The plastomes of seven Potamogetonaceae species (six Potamogeton and one Stuckenia species) ranged from 155,863 bp (P.crispus) to 156,669 bp (S.pectinata).The seven Potamogetonaceae plastomes displayed a typical quadripartite structure, consisting of a pair of IRs (25,585-26,073 bp) separated by LSC (86,191-86,898 bp) and SSC (18,182-18,286 bp) regions (Figure 1, Table 1).The overall GC content was consistent (36.5%) in the seven Potamogetonaceae species.The seven Potamogetonaceae plastomes contained 113 genes, i.e., 79 protein-coding genes, 30 tRNA genes, and 4 rRNA genes.The IR regions of P. wrightii, P. distinctus, and P.perfoliatus had 17 genes (trnN-GUU, trnR-ACG, trnA-GAU, trnI-GAU, trnV-GAC, trnL-CAA, trnM-AUG, rrn4.5, rrn5, rrn23, rrn16, rpl2, rpl23, rps7, ndhB, ycf1, and ycf2), whereas those of P. crispus, P. maackianus, and S. pectinatus had 18 genes due to IR expansion, in which trnH gene was included in the IR region of the three plastomes.The boundaries between the IR and single-copy (SC) regions of the six Potamogeton plastomes and the single Stuckenia plastome were compared (Figure 2).While the IRb/SSC boundary was similar in all Potamogeton species, the LSC/IRb boundary was located between rps19 and rpl2 regions in three species (P.distincus, P. wirghtii, and P. perfoliatus), whereas it was between rps19 and trnH in the P. crispus, P. maackianus, and S. pectinatus plastomes.Five species (P.distincus, P. wirghtii, P. perfoliatus, P. maackianus, and S. pectinatus) had overlapping ycf1 and ndhF genes, and the overlapped region between ycf1 and ndhF ranged from 8 to 29 bp in length.The IRb/SSC boundary in P. crispus did not overlap The boundaries between the IR and single-copy (SC) regions of the six Potamogeton plastomes and the single Stuckenia plastome were compared (Figure 2).While the IRb/SSC boundary was similar in all Potamogeton species, the LSC/IRb boundary was located between rps19 and rpl2 regions in three species (P.distincus, P. wirghtii, and P. perfoliatus), whereas it was between rps19 and trnH in the P. crispus, P. maackianus, and S. pectinatus plastomes.Five species (P.distincus, P. wirghtii, P. perfoliatus, P. maackianus, and S. pectinatus) had overlapping ycf1 and ndhF genes, and the overlapped region between ycf1 and ndhF ranged from 8 to 29 bp in length.The IRb/SSC boundary in P. crispus did not overlap the ycf1 and ndhF genes.The SSC/IRa boundary was located in the ycf1 gene in all Potamogeton species.The IRa/LSC boundary was located at the trnH gene in three species (P.wrightii, P. distinctus, and P. perfoliatus) and three species (P.crispus, P. maackianus and S. pectinatus) had trnH genes in the IRa region.The 6 kb inversion previously reported from P. perfoliatus was found in all Potamogetonaceae plastomes (Figure 1). the ycf1 and ndhF genes.The SSC/IRa boundary was located in the ycf1 gene in all Potamogeton species.The IRa/LSC boundary was located at the trnH gene in three species (P.wrightii, P. distinctus, and P. perfoliatus) and three species (P.crispus, P. maackianus and S. pectinatus) had trnH genes in the IRa region.The 6 kb inversion previously reported from P. perfoliatus was found in all Potamogetonaceae plastomes (Figure 1).
Four types of repeats (forward, reverse, complement, and palindromic) were found in the Potamogetonaceae plastomes (Figure 3B).The number of tandem repeats ranged
from 34 (P.maakianus) to 38 (P.perfoliatus).Five Potamogeton species had 16 forward repeats, whereas P. cirspus had 17.Eighteen palindromic repeats were found in all the Potamogetonaceae plastomes.Three species (P.crispus, P. maakianus, and S. pectinate) had one reverse repeat, two species (P.wrightii and P. distinctus) had two reverse repeats, and P. perfoliatus had four reverse repeats in their plastomes.Complement repeats were found only in the P. distinctus plastome.

Divergence Regions in the Potamogetonaceae Plastomes
Whole plastomes within the family Potamogetonaceae (genera Potamogeton and Stuckenia) and within the genus Potamogeton were compared.The LSC and SSC regions showed a much higher variation than did the IR region.Among the Potamogetonaceae plastomes, the values ranged from 0 to 0.04286 (Figure 4a).Five regions, rps16-trnQ, rpoB-trnC, trnC-psbM, ndhF-rpl32, and the atpF intron showed higher nucleotide diversity (Pi) values than did other regions in their plastomes.Among the five Potamogeton plastomes, the Pi values ranged from 0 to 0.02156 (Figure 4b) and five regions (rps16-trnQ, the atpF intron, petN-trnD, ccsA-ndhD, and ycf1) were found to be divergence regions.Four types of repeats (forward, reverse, complement, and palindromic) were found in the Potamogetonaceae plastomes (Figure 3B).The number of tandem repeats ranged from 34 (P.maakianus) to 38 (P.perfoliatus).Five Potamogeton species had 16 forward repeats, whereas P. cirspus had 17.Eighteen palindromic repeats were found in all the Potamogetonaceae plastomes.Three species (P.crispus, P. maakianus, and S. pectinate) had one reverse repeat, two species (P.wrightii and P. distinctus) had two reverse repeats, and P. perfoliatus had four reverse repeats in their plastomes.Complement repeats were found only in the P. distinctus plastome.

Divergence Regions in the Potamogetonaceae Plastomes
Whole plastomes within the family Potamogetonaceae (genera Potamogeton and Stuckenia) and within the genus Potamogeton were compared.The LSC and SSC regions showed a much higher variation than did the IR region.Among the Potamogetonaceae plastomes, the values ranged from 0 to 0.04286 (Figure 4a).Five regions, rps16-trnQ, rpoB-trnC, trnC-psbM, ndhF-rpl32, and the atpF intron showed higher nucleotide diversity (Pi) values than did other regions in their plastomes.Among the five Potamogeton plastomes, the Pi values ranged from 0 to 0.02156 (Figure 4b) and five regions (rps16-trnQ, the atpF intron, petN-trnD, ccsA-ndhD, and ycf1) were found to be divergence regions.

Comparative Analyses of the Plastomes among Alismatales
Twenty complete plastomes of Alismatales ranged from 154,516 bp (Aponogeton de torum) to 179,007 bp (Sagittaria lichunanensis) (Table 1).The S. lichunanensis plastome the longest LSC and a shorter SSC region compared with those of the plastomes of o species.The overall GC content was comparable, ranging from 36.8% (S. lichuanensis 38.2% (Najas flexilis).Most plastomes of Alismatales contained 113 genes (79 protein-c ing genes, 30 tRNA genes, and 4 rRNA genes).However, the plastid NAD(P)H dehyd genase (NDH) complex was lost in the N. flexilis plastome.The genome structure and g order of the Alismatales plastomes are conserved.However, the S. lichiuanensis plasto revealed an inversion of the psbK-trnS region, and a 6 kb inversion was detected in plastomes of Sytingodium isoetifolium, and Ruppia brevipedunculata (Figures 1 and 5).F types of IR/SC junctions were found in Alismatales (Figure 4).Most Alismatales plasto had the type 3 junction.The LSC/IRa and LSC/IRb junctions were located in the rps19region and the psbA-rpl2 region, respectively.The SSC/IRa and SSC/IRb junctions w located in the ψycf1 and the ndhF-ycf1 region, respectively.

Comparative Analyses of the Plastomes among Alismatales
Twenty complete plastomes of Alismatales ranged from 154,516 bp (Aponogeton desertorum) to 179,007 bp (Sagittaria lichunanensis) (Table 1).The S. lichunanensis plastome had the longest LSC and a shorter SSC region compared with those of the plastomes of other species.The overall GC content was comparable, ranging from 36.8% (S. lichuanensis) to 38.2% (Najas flexilis).Most plastomes of Alismatales contained 113 genes (79 protein-coding genes, 30 tRNA genes, and 4 rRNA genes).However, the plastid NAD(P)H dehydrogenase (NDH) complex was lost in the N. flexilis plastome.The genome structure and gene order of the Alismatales plastomes are conserved.However, the S. lichiuanensis plastome revealed an inversion of the psbK-trnS region, and a 6 kb inversion was detected in the plastomes of Sytingodium isoetifolium, and Ruppia brevipedunculata (Figures 1 and 5).Four types of IR/SC junctions were found in Alismatales (Figure 4).Most Alismatales plastomes had the type 3 junction.The LSC/IRa and LSC/IRb junctions were located in the rps19-rpl2 region and the psbA-rpl2 region, respectively.The SSC/IRa and SSC/IRb junctions were located in the ψycf1 and the ndhF-ycf1 region, respectively.

Phylogenetic Analysis
Due to the numerous gene losses in the cp genomes of Najas flexilis (13 genes including 11 ndh genes, infA, and psbH) and A. gramineus (accD), in total, 65 shared protein-coding genes were used to reconstruct the phylogenetic relationships of Alismatales (Figure 6; Supplementary Material Table S1).The topologies obtained from the ML and BI trees were consistent.As a result, Alismatales was divided into two groups: (1) Alismataceae (Sagittaria) and Hydrocharitaceae (Najas, Elodea, Blyxa, and Ottelia), and ( 2

Phylogenetic Analysis
Due to the numerous gene losses in the cp genomes of Najas flexilis (13 genes including 11 ndh genes, infA, and psbH) and A. gramineus (accD), in total, 65 shared protein-coding genes were used to reconstruct the phylogenetic relationships of Alismatales (Figure 6; Supplementary Material Table S1).The topologies obtained from the ML and BI trees were consistent.As a result, Alismatales was divided into two groups: (1) Alismataceae (Sagittaria) and Hydrocharitaceae (Najas, Elodea, Blyxa, and Ottelia), and ( 2

Nucleotide Substitution Rate Analyses
In total, 48 shared protein-coding genes of 21 Alismatales plastomes, including thpse of 7 Potamogetonaceae were used to estimate the synonymous (dS) and nonsynonymous (dN) nucleotide substitution rates (Figure 7).The mean dS of the Alismatales plastomes was higher than the mean dN.While the dN/dS ratio of most genes was less than 1, the dN/dS ratios of the rps15 gene in the plastomes of Tofieldia thibetica, S. lichuanensis, N. flexilis, A. desertorum, and A. madagascariensis were 1.663, 1.4746, 1.0597, 1.002, and 1.002, respectively, and that of ClpP in N. flexilis was 1.149.All Potamogetonaceae plastomes including Stuckia and Potamogeton showed a dN/dS ratio of less than 1.The dS of the Potamogetonaceae plastomes ranged from 0 to 0.77, the dN ranged from 0 to 0.1366, and the dN/dS ratio ranged from 0.0263 to 0.822.

Nucleotide Substitution Rate Analyses
In total, 48 shared protein-coding genes of 21 Alismatales plastomes, including thpse of 7 Potamogetonaceae were used to estimate the synonymous (dS) and nonsynonymous (dN) nucleotide substitution rates (Figure 7).The mean dS of the Alismatales plastomes was higher than the mean dN.While the dN/dS ratio of most genes was less than 1, the dN/dS ratios of the rps15 gene in the plastomes of Tofieldia thibetica, S. lichuanensis, N. flexilis, A. desertorum, and A. madagascariensis were 1.663, 1.4746, 1.0597, 1.002, and 1.002, respectively, and that of ClpP in N. flexilis was 1.149.All Potamogetonaceae plastomes including Stuckia and Potamogeton showed a dN/dS ratio of less than 1.The dS of the Potamogetonaceae plastomes ranged from 0 to 0.77, the dN ranged from 0 to 0.1366, and the dN/dS ratio ranged from 0.0263 to 0.822.

Nucleotide Substitution Rate Analyses
In total, 48 shared protein-coding genes of 21 Alismatales plastomes, including thpse of 7 Potamogetonaceae were used to estimate the synonymous (dS) and nonsynonymous (dN) nucleotide substitution rates (Figure 7).The mean dS of the Alismatales plastomes was higher than the mean dN.While the dN/dS ratio of most genes was less than 1, the dN/dS ratios of the rps15 gene in the plastomes of Tofieldia thibetica, S. lichuanensis, N. flexilis, A. desertorum, and A. madagascariensis were 1.663, 1.4746, 1.0597, 1.002, and 1.002, respectively, and that of ClpP in N. flexilis was 1.149.All Potamogetonaceae plastomes including Stuckia and Potamogeton showed a dN/dS ratio of less than 1.The dS of the Potamogetonaceae plastomes ranged from 0 to 0.77, the dN ranged from 0 to 0.1366, and the dN/dS ratio ranged from 0.0263 to 0.822.

Discussion
The six Potamogeton plastomes measured approximately 156 kb in length and consistent gene content (79 protein-coding genes, 30 tRNA genes, and 4 rRNA genes).Luo et al. [49] found a 6 kb inversion in the P. perfoliatus plastome.By comparing the genome structure of the Potamogetonaceae (Potamogeton and Stuckenia) and Alismatale plastomes, we found the 6 kb inversion in all Potamogetonaceae plastomes (Figures 1 and 6).The 6 kb inversion was also detected in the Syringodium (Cymodaceae) and Ruppia (Ruppiaceae) plastomes (Figure 5).Previous studies [61][62][63][64] suggested that inversion is likely caused by the intramolecular recombination of the repeats, and Fullerton et al. [65] suggested that G + C content affects the plastome structure.However, we did not find any evidence that the repeats or G + C content were associated with the 6 kb inversion in the Alismatales plastomes (Figure 2, Table 1).
IR expansion and construction in plastomes have been reported from diverse angiosperm lineages, such as Passifloraceae, Fabiaceae, Geraniaceae, Campanulaceae, and Poaceae [31,35,[66][67][68].The IR/SC junctions of the Potamogetonaceae plastomes can be divided into two types: (1) trnH in the LSC/IR junction type and (2) trnH in the IR region type (Figures 2 and 4).trnH duplication was previously reported in Elaeagnaceae [69] and monocots [70], and it was hypothesized to have IR expansion [70].First, double-strand break (DSB) events occur within the IR regions, and then the free 3 end of the broken strand is repaired against the homologous sequence in the IR regions.We speculated that the IRb region was expanded to the trnH gene, which was duplicated in the IRa region via a copy correction mechanism.The S. lichuanensis plastome showed different IR expansions, with DSB events occurring within the IRa region and an expansion of the IRa region to the SSC (ndhH) region.Subsequently, a duplication of the ndhH gene in the newly repaired IRb was achieved.
Previous studies have suggested that the genus Stuckenia should be distinguished from the genus Potamogeton [6,16,73], whereas Wiegleb and Kaplan [11] did not support this.Our study revealed that the genus Potamogeton is monophyletic and sister to Stuckenia pectinate (Figure 6).This result also supports the taxonomic treatment of two independent genera, Stuckenia and Potamogeton.The phylogenetic relationship of Potamogeton was not resolved in previous studies [16,17,20,74].All molecular phylogenetic studies of Potamogeton used a few plastid genes, including psbA-trnH, trnT-L, the trnL intron, trnL-trnF, rbcL, and nrDNA ITS regions, resulting in uncertain species delimitations of Potamogeton species.For example, Iida et al. [17] showed that the genus Potamogeton could be divided into two groups.However, they failed to distinguish between Potamogeton gramineus and P. perfoliatus, because these two species formed a clade together.Moreover, Aykurt et al. [20] suggested a sister relationship between P. perfoliatus and P. nodosus, whereas P. perfoliatus formed a clade with P. richardsonii and the clade was sister to the clade of P. wrightii, P. distinctus, P. illinoensis, and P. nodosus [74].Our study showed that P. perfoliatus was sister to the clade of P. wrightii and P. distinctus (Figure 6).Due to the insertion in the trnL-trnF region, P. crispus was distant from P. maackianus, but these two species were shown to have a sister relationship in the phylogeny by Ito et al. [74].In this study, the sister relationship between P. crispus and P. maackianus was reconstructed and supported the findings of the previous study [74].These differences may have been caused by the misidentification of the species owing to the similar morphological characteristics and hybridization of the species.Alternatively, they may have been caused by the insufficient molecular data for the phylogenetic reconstruction of the genus Potamogeton.Our study suggested five regions for the phylogenetic reconstruction and species identification of the genus Potamogeton.The five regions, rps16-trnQ, the atpF intron, petN-trnD, ccsA-ndhD, and ycf1 have not been used for Potamogeton so far, but the five regions will be used as valuable resources for determining the taxonomy and phylogenetics of the genus Potamogeton.
Synonymous and nonsynonymous rates provide evidence to understand the evolutionary forces in a gene [75].The dN/dS ratio indicates the selection pressures.If the dN/dS ratio is higher than 1, the gene is under a positive selection, whereas if the ratio is less than 1, the gene is under a purifying selection [76].We found two genes, rps15 (T.thibetica, S. lichuanensis, N. flexilis, A. desertorum, and Aponogeton madagascariensis) and clpP (N.flexilis), which are under positive selection in the Alismatales plastomes (Figure 7).It has been reported that the substitution rates of the gene in the IR regions were relatively lower than those in the two SC (LSC and SSC) regions.However, the genes in the expanded IR regions did not show any reduction in substitution rates [33,47,77].Our study also showed that the substitution rates of the rps15 gene, which was relocated from the SSC to the IR regions in the S. lichuanensis plastome, were higher than those of the genes in the IR region (Figure 7).The Potamogeton plastomes exhibited a purifying selection (dN/dS < 1) for all genes.

Conclusions
Our study provides five newly assembled plastomes of the Potamogeton species.Comparative genomics of the Potamogeton plastomes showed that their genomes were conserved in genome size (155,863 bp-156,488 bp) and GC content (36.5%).However, IR boundary variation, such as trnH duplication, was detected in the P. crispus and P. maakianus plastomes.Five regions (rps16-trnQ, the atpF intron, rpoB-trnC, trnC-psbM, and ndhF-rpl32) were identified for phylogenetic and taxonomic studies of Potamogeton.Comparative genomics of the Alismatales plastomes showed that the Potamogetonaceae, Cymodaceae, and Ruppiaceae plastomes had the 6 kb inversion, and that the trnH duplication had occurred in the IR region of the Stuckenia pectinate plastome.Our phylogenomic studies using 48 shared protein-coding genes showed that Potamogetonaceae (Potamogeton and Stuckenia) was monophyletic.The synonymous and non-synonymous rates showed that the genes of the Potamogeteon plastomes were under purifying selection (dN/dS < 1).

Figure 1 .
Figure 1.Gene map of Potamogeton plastid genomes.(a) Plastid genomes of P. crispus and P. maackianus.(b) Plastid genomes of P. wrightii, P. distinctus and P. perfoliatus.Genes drawn inside the circle are transcribed clockwise, and those outside are transcribed counterclockwise.The darker gray in the inner circle corresponds to GC contents.

Figure 1 .
Figure 1.Gene map of Potamogeton plastid genomes.(a) Plastid genomes of P. crispus and P. maackianus.(b) Plastid genomes of P. wrightii, P. distinctus and P. perfoliatus.Genes drawn inside the circle are transcribed clockwise, and those outside are transcribed counterclockwise.The darker gray in the inner circle corresponds to GC contents.

Figure 4 .
Figure 4. Comparison of the nucleotide variability (Pi) values (a) compared among Potamoget ceae species and (b) compared among Potamogeton species.

Figure 4 .
Figure 4. Comparison of the nucleotide variability (Pi) values (a) compared among Potamogetonaceae species and (b) compared among Potamogeton species.

Figure 5 .
Figure 5. (a) The phylogenetic trees were constructed based on 65 coding genes of 21 Alismatales plastomes.(b) Types of junction between large single-copy (LSC), small single-copy (SSC), and IR regions in the Alismatales plastomes.

Figure 5 .
Figure 5. (a) The phylogenetic trees were constructed based on 65 coding genes of 21 Alismatales plastomes.(b) Types of junction between large single-copy (LSC), small single-copy (SSC), and IR regions in the Alismatales plastomes.

Figure 6 .
Figure 6.Phylogenetic tree constructed using the maximum likelihood (ML) and Baysian inference (BI) methods based on 65 plastid protein-coding genes.The number above the lines indicates bootstrap values/BI posterior probabilities.

Figure 6 .
Figure 6.Phylogenetic tree constructed using the maximum likelihood (ML) and Baysian inference (BI) methods based on 65 plastid protein-coding genes.The number above the lines indicates bootstrap values/BI posterior probabilities.

Genes 2023 , 14 Figure 6 .
Figure 6.Phylogenetic tree constructed using the maximum likelihood (ML) and Baysian inference (BI) methods based on 65 plastid protein-coding genes.The number above the lines indicates bootstrap values/BI posterior probabilities.

Table 1 .
Comparison of the plastid genome features of Potagometon species.