The Chloroplast Genome of Symplocarpus renifolius: A Comparison of Chloroplast Genome Structure in Araceae

The complete chloroplast genome sequence of Lemna turionifera (Araceae)

Lemna turionifera is native to North America and northern Asia, with significant potential for industrial wastewater remediation. The complete nucleotide sequence of the L. turionifera chloroplast genome (cpDNA) was determined. The cpDNA is a circular molecule of 166,606 bp and containing a pair of inverted repeats (IRs) measuting 31,663 bp each. These IRs are flanked by a small single-copy region of 13,542 bp and a large single-copy region of 89,738 bp. The chloroplast genome of L. turionifera consisted of 112 unique genes, including 78 protein-encoding genes, 30 tRNA genes, and four rRNA genes. The phylogenetic analysis utilizing cpDNA provided a well-supported resolution of the relationships among subfamilies within the Araceae family. Our findings indicated a close relationship between L. turionifera and a clade consisting of L. minor, L. japonica, and L. gibba. The availability of the complete chloroplast genome sequence of L. turionifera presents valuable data for future phylogenetic investigations within the Lemnaceae family.

Complete chloroplast genome of the Malus baccata var. gracilis provides insights into the evolution and phylogeny of Malus species

Malus baccata (L.) var. gracilis (Rehd.) has high ornamental value and breeding significance, and comparative chloroplast genome analysis was applied to facilitate genetic breeding for desired traits and resistance and provide insight into the phylogeny of this genus. Using data from whole-genome sequencing, a tetrameric chloroplast genome with a length of 159,992 bp and a total GC content of 36.56% was constructed. The M. baccata var. gracilis chloroplast genome consists of a large single-copy sequence (88,100 bp), a short single-copy region (19,186 bp), and two inverted repeat regions, IRa (26,353 bp) and IRb (26,353 bp). This chloroplast genome contains 112 annotated genes, including 79 protein-coding genes (nine multicopy), 29 tRNA genes (eight multicopy), and four rRNA genes (all multicopy). Calculating the relative synonymous codon usage revealed a total of 32 high-frequency codons, and the codons exhibited a biased usage pattern towards A/U as the ending nucleotide. Interspecific sequence comparison and boundary analysis revealed significant sequence variation in the vast single-copy region, as well as generally similar expansion and contraction of the SSC and IR regions for 10 analyzed Malus species. M. baccata var. gracilis and Malus hupehensis were grouped together into one branch based on phylogenetic analysis of chloroplast genome sequences. The chloroplast genome of Malus species provides an important foundation for species identification, genetic diversity analysis, and Malus chloroplast genetic engineering. Additionally, the results can facilitate the use of pendant traits to improve apple tree shape.

The complete chloroplast genome of Diplodiscus trichospermus and phylogenetic position of Brownlowioideae within Malvaceae

BACKGROUND

Malvaceae is an economically important plant family of 4,225 species in nine subfamilies. Phylogenetic relationships among the nine subfamilies have always been controversial, especially for Brownlowioideae, whose phylogenetic position remains largely unknown due to the lack of samples in previous analysis datasets. To greatly clarify the phylogenetic relationship of Malvaceae, we newly sequenced and assembled the plastome of Diplodiscus trichospermus taxonomically located in Brownlowioideae, and downloaded the allied genomes from public database to build a dataset covering all subfamily members of Malvaceae.

RESULTS

The annotation results showed that the plastome of Diplodiscus trichospermus has a typical quadripartite structure, comprising 112 unique genes, namely 78 protein-coding genes, 30 tRNA genes and 4 rRNA genes. The total length was 158,570 bp with 37.2% GC content. Based on the maximum likelihood method and Bayesian inference, a robust phylogenetic backbone of Malvaceae was reconstructed. The topology showed that Malvaceae was divided distinctly into two major branches which were previously recognized as Byttneriina and Malvadendrina. In the Malvadendrina clade, Malvoideae and Bombacoideae formed, as always, a close sister clade named as Malvatheca. Subfamily Helicteroideae occupied the most basal position and was followed by Sterculioideae which was sister to the alliance of Malvatheca, Brownlowioideae, Dombeyoideae, and Tilioideae. Brownlowioideae together with the clade comprising Dombeyoideae and Tilioideae formed a sister clade to Malvatheca. In addition, one specific conservation SSR and three specific palindrome sequences were observed in Brownlowioideae.

CONCLUSIONS

In this study, the phylogenetic framework of subfamilies in Malvaceae has been resolved clearly based on plastomes, which may contribute to a better understanding of the classification and plastome evolution for Malvaceae.

Potential contribution of floral thermogenesis to cold adaptation, distribution pattern, and population structure of thermogenic and non/slightly thermogenic Symplocarpus species

The genus Symplocarpus in basal Araceae includes both thermogenic and non/slightly thermogenic species that prefer cold environments. If floral thermogenesis of Symplocarpus contributes to cold adaptation, it would be expected that thermogenic species have a larger habitat than non/slightly thermogenic species during an ice age, leading to increased genetic diversity in the current population. To address this question, potential distribution in past environment predicted by ecological niche modeling (ENM), genetic diversity, and population structure of chloroplast and genome-wide single nucleotide polymorphisms were compared between thermogenic Symplocarpus renifolius and non/slightly thermogenic Symplocarpus nipponicus. ENM revealed that the distribution of S. nipponicus decreased, whereas that of S. renifolius expanded in the Last Glacial Maximum. Phylogeographic analyses have shown that the population structures of the two species were genetically segmented and that the genetic diversity of S. renifolius was higher than that of S. nipponicus. The phylogenetic relationship between chloroplast and nuclear DNA is topologically different in the two species, which may be due to the asymmetric gene flow ubiquitously observed in plants. The results of this study imply that floral thermogenesis of Symplocarpus contributes to expanding the distribution during an ice age, resulting in increased genetic diversity due to cold adaptation.

Comparative chloroplast genomes and phylogenetic relationships of Aglaonema modestum and five variegated cultivars of Aglaonema

Aglaonema, commonly called Chinese evergreens, are widely used for ornamental purposes. However, attempts to identify Aglaonema species and cultivars based on leaf morphology have been challenging. In the present study, chloroplast sequences were used to elucidate the phylogenetic relationships of cultivated Aglaonema in South China. The chloroplast genomes of one green species and five variegated cultivars of Aglaonema, Aglaonema modestum, ‘Red Valentine’, ‘Lady Valentine’, ‘Hong Yan’, ‘Hong Jian’, and ‘Red Vein’, were sequenced for comparative and phylogenetic analyses. The six chloroplast genomes of Aglaonema had typical quadripartite structures, comprising a large single copy (LSC) region (91,092–91,769 bp), a small single copy (SSC) region (20,816–26,501 bp), and a pair of inverted repeat (IR) regions (21,703–26,732 bp). The genomes contained 112 different genes, including 79–80 protein coding genes, 28–29 tRNAs and 4 rRNAs. The molecular structure, gene order, content, codon usage, long repeats, and simple sequence repeats (SSRs) were generally conserved among the six sequenced genomes, but the IR-SSC boundary regions were significantly different, and ‘Red Vein’ had a distinct long repeat number and type frequency. For comparative and phylogenetic analyses, Aglaonema costatum was included; it was obtained from the GenBank database. Single-nucleotide polymorphisms (SNPs) and insertions/deletions (indels) were determined among the seven Aglaonema genomes studied. Nine divergent hotspots were identified: trnH-GUG-CDS1_psbA, trnS-GCU_trnS-CGA-CDS1, rps4-trnT-UGU, trnF-GAA-ndhJ, petD-CDS2-rpoA, ycf1-ndhF, rps15-ycf1-D2, ccsA-ndhD, and trnY-GUA-trnE-UUC. Additionally, positive selection was found for rpl2, rps2, rps3, ycf1 and ycf2 based on the analyses of Ka/Ks ratios among 16 Araceae chloroplast genomes. The phylogenetic tree based on whole chloroplast genomes strongly supported monophyletic Aglaonema and clear relationships among Aroideae, Lasioideae, Lemnoideae, Monsteroideae, Orontioideae, Pothoideae and Zamioculcadoideae in the family Araceae. By contrast, protein coding gene phylogenies were poorly to strongly supported and incongruent with the whole chloroplast genome phylogenetic tree. This study provided valuable genome resources and helped identify Aglaonema species and cultivars.

The Complete Chloroplast Genome of Endangered Species Stemona parviflora: Insight into the Phylogenetic Relationship and Conservation Implications

Stemona parviflora is an endangered species, narrowly endemic to Hainan and Southwest Guangdong. The taxonomic classification of S. parviflora remains controversial. Moreover, studying endangered species is helpful for current management and conservation. In this study, the first complete chloroplast genome of S. parviflora was assembled and compared with other Stemona species. The chloroplast genome size of S. parviflora was 154,552 bp, consisting of 87 protein-coding genes, 38 tRNA genes, 8 rRNA genes, and one pseudogene. The ψycf1 gene was lost in the cp genome of S. sessilifolia, but it was detected in four other species of Stemona. The inverted repeats (IR) regions have a relatively lower length variation compared with the large single copy (LSC) and small single copy (SSC) regions. Long repeat sequences and simple sequence repeat (SSR) were detected, and most SSR were distributed in the LSC region. Codon usage bias analyses revealed that the RSCU value of the genus Stemona has almost no difference. As with most angiosperm chloroplast genomes, protein-coding regions were more conservative than the inter-gene spacer. Seven genes (atpI, ccsA, cemA, matK, ndhA, petA, and rpoC1) were detected under positive selection in different Stemona species, which may result from adaptive evolution to different habitats. Phylogenetic analyses show the Stemona cluster in two main groups; S. parviflora were closest to S. tuberosa. A highly suitable region of S. parviflora was simulated by Maxent in this study; it is worth noting that the whole territory of Taiwan has changed to a low fitness area and below in the 2050 s, which may not be suitable for the introduction and cultivation of S. parviflora. In addition, limited by the dispersal capacity of S. parviflora, it is necessary to carry out artificial grafts to expand the survival areas of S. parviflora. Our results provide valuable information on characteristics of the chloroplast genome, phylogenetic relationships, and potential distribution range of the endangered species S. parviflora.

The Ribosomal DNA Loci of the Ancient Monocot Pistia stratiotes L. (Araceae) Contain Different Variants of the 35S and 5S Ribosomal RNA Gene Units

The freshwater plant water lettuce (Pistia stratiotes L.) grows in warm climatic zones and is used for phytoremediation and biomass production. P. stratiotes belongs to the Araceae, an ecologically and structurally diverse early monocot family, but the phylogenetic relationships among Araceae members are poorly understood. Ribosomal DNAs (rDNAs), including the 35S and 5S rDNA, encode the RNA components of ribosomes and are widely used in phylogenetic and evolutionary studies of various plant taxa. Here, we comprehensively characterized the chromosomal locations and molecular organization of 35S and 5S rDNA genes in water lettuce using karyological and molecular methods. Fluorescence in situ hybridization revealed a single location for the 35S and 5S rDNA loci, each on a different pair of the species' 28 chromosomes. Molecular cloning and nucleotide sequencing of 35S rDNA of P. stratiotes, the first representative Araceae sensu stricto in which such a study was performed, displayed typical structural characteristics. The full-length repeat showed high sequence conservation of the regions producing the 18S, 5.8S, and 25S rRNAs and divergence of the internal transcribed spacers ITS1 and ITS2 as well as the large intergenic spacer (IGS). Alignments of the deduced sequence of 18S rDNA with the sequences available for other Araceae and representatives of other clades were used for phylogenetic analysis. Examination of 11 IGS sequences revealed significant intra-genomic length variability due to variation in subrepeat number, with four types of units detected within the 35S rDNA locus of the P. stratiotes genome (estimated size 407 Mb/1C). Similarly, the 5S rDNA locus harbors gene units comprising a conserved 119-bp sequence encoding 5S rRNA and two types of non-transcribed spacer (NTS) sequences. Type I was classified into four subtypes, which apparently originated via progressive loss of subrepeats within the duplicated NTS region containing the 3' part of the 5S rRNA gene. The minor Type II NTS is shorter than Type I and differs in nucleotide composition. Some DNA clones containing two or three consecutive 5S rDNA repeats harbored 5S rDNA genes with different types of NTSs, confirming the mosaic composition of the 5S rDNA locus.

Lemnaceae and Orontiaceae Are Phylogenetically and Morphologically Distinct from Araceae

Duckweeds comprise a distinctive clade of pleustophytic monocots that traditionally has been classified as the family Lemnaceae. However, molecular evidence has called into question their phylogenetic independence, with some authors asserting instead that duckweeds should be reclassified as subfamily Lemnoideae of an expanded family Araceae. Although a close phylogenetic relationship of duckweeds with traditional Araceae has been supported by multiple studies, the taxonomic disposition of duckweeds must be evaluated more critically to promote nomenclatural stability and utility. Subsuming duckweeds as a morphologically incongruent lineage of Araceae effectively eliminates the family category of Lemnaceae that has been widely used for many years. Instead, we suggest that Araceae subfamily Orontioideae should be restored to family status as Orontiaceae, which thereby would enable the recognition of three morphologically and phylogenetically distinct lineages: Araceae, Lemnaceae, and Orontiaceae.

Mutational Dynamics of Aroid Chloroplast Genomes II

The co-occurrence among single nucleotide polymorphisms (SNPs), insertions-deletions (InDels), and oligonucleotide repeats has been reported in prokaryote, eukaryote, and chloroplast genomes. Correlations among SNPs, InDels, and repeats have been investigated in the plant family Araceae previously using pair-wise sequence alignments of the chloroplast genomes of two morphotypes of one species, Colocasia esculenta belonging to subfamily Aroideae (crown group), and four species from the subfamily Lemnoideae, a basal group. The family Araceae is a large family comprising 3,645 species in 144 genera, grouped into eight subfamilies. In the current study, we performed 34 comparisons using 27 species from 7 subfamilies of Araceae to determine correlation coefficients among the mutational events at the family, subfamily, and genus levels. We express strength of the correlations as: negligible or very weak (0.10–0.19), weak (0.20–0.29), moderate (0.30–0.39), strong (0.40–0.69), very strong (0.70–0.99), and perfect (1.00). We observed strong/very strong correlations in most comparisons, whereas a few comparisons showed moderate correlations. The average correlation coefficient was recorded as 0.66 between “SNPs and InDels,” 0.50 between “InDels and repeats,” and 0.42 between “SNPs and repeats.” In qualitative analyses, 95–100% of the repeats at family and sub-family level, while 36–86% of the repeats at genus level comparisons co-occurred with SNPs in the same bins. Our findings show that such correlations among mutational events exist throughout Araceae and support the hypothesis of distribution of oligonucleotide repeats as a proxy for mutational hotspots.

Chloroplast genome evolution in the Dracunculus clade (Aroideae, Araceae)

Chloroplast (cp) genomes are considered important for the study of lineage-specific molecular evolution, population genetics, and phylogenetics. Our aim here was to elucidate the molecular evolution in cp genomes of species in the Dracunculus clade (Aroideae, Araceae). We report de novo assembled cp genomes for eight species from eight genera and also retrieved cp genomes of four species from the National Center for Biotechnology Information (NCBI). The cp genomes varied in size from 162,424 bp to 176,835 bp. Large Single Copy (LSC) region ranged in size from 87,141 bp to 95,475 bp; Small Single Copy (SSC) from 14,338 bp to 23,981 bp; and Inverted Repeats (IRa and IRb) from 25,131 bp to 32,708 bp. The expansion in inverted repeats led to duplication of ycf1 genes in four species. The genera showed high similarity in gene content and yielded 113 unique genes (79 protein-coding, 4 rRNA, and 30 tRNA genes). Codon usage, amino acid frequency, RNA editing sites, microsatellites repeats, transition and transversion substitutions, and synonymous and non-synonymous substitutions were also similar across the clade. A previous study reported deletion of ycf1, accD, psbE, trnL-CAA, and trnG-GCC genes in four Amorphophallus species. Our study supports conservative structure of cp genomes in the Dracunculus clade including Amorphophallus species and does not support gene deletion mentioned above. We also report suitable polymorphic loci based on comparative analyses of Dracunculus clade species, which could be useful for phylogenetic inference. Overall, the current study broad our knowledge about the molecular evolution of chloroplast genome in aroids.

Phylogenetic and Comparative Analyses of Complete Chloroplast Genomes of Chinese Viburnum and Sambucus (Adoxaceae)

Phylogenetic analyses of complete chloroplast genome sequences have yielded significant improvements in our understanding of relationships in the woody flowering genus Viburnum (Adoxaceae, Dipsacales); however, these relationships were evaluated focusing only on Viburnum species within Central and South America and Southeast Asia. By contrast, despite being a hotspot of Viburnum diversity, phylogenetic relationships of Viburnum species in China are less well known. Here, we characterized the complete chloroplast (cp) genomes of 21 Viburnum species endemic to China, as well as three Sambucus species. These 24 plastomes were highly conserved in genomic structure, gene order and content, also when compared with other Adoxaceae. The identified repeat sequences, simple sequence repeats (SSRs) and highly variable plastid regions will provide potentially valuable genetic resources for further population genetics and phylogeographic studies on Viburnum and Sambucus. Consistent with previous combined phylogenetic analyses of 113 Viburnum species, our phylogenomic analyses based on the complete cp genome sequence dataset confirmed the sister relationship between Viburnum and the Sambucus-Adoxa-Tetradoxa-Sinadoxa group, the monophyly of four recognized sections in Flora of China (i.e., Viburnum sect. Tinus, Viburnum sect. Solenotinus, Viburnum sect. Viburnum and Viburnum sect. Pseudotinus) and the nonmonophyly of Viburnum sect. Odontotinus and Viburnum sect. Megalotinus. Additionally, our study confirmed the sister relationships between the clade Valvatotinus and Viburnum sect. Pseudotinus, as well as between Viburnum sect. Opulus and the Odontotinus-Megalotinus group. Overall, our results clearly document the power of the complete cp genomes in improving phylogenetic resolution, and will contribute to a better understanding of plastome evolution in Chinese Adoxaceae.

Complete Chloroplast Genomes of Anthurium huixtlense and Pothos scandens (Pothoideae, Araceae): Unique Inverted Repeat Expansion and Contraction Affect Rate of Evolution

The subfamily Pothoideae belongs to the ecologically important plant family Araceae. Here, we report the chloroplast genomes of two species of the subfamily Pothoideae: Anthurium huixtlense (size: 163,116 bp) and Pothos scandens (size: 164,719 bp). The chloroplast genome of P. scandens showed unique contraction and expansion of inverted repeats (IRs), thereby increasing the size of the large single-copy region (LSC: 102,956 bp) and decreasing the size of the small single-copy region (SSC: 6779 bp). This led to duplication of many single-copy genes due to transfer to IR regions from the small single-copy (SSC) region, whereas some duplicate genes became single copy due to transfer to large single-copy regions. The rate of evolution of protein-coding genes was affected by the contraction and expansion of IRs; we found higher mutation rates for genes that exist in single-copy regions as compared to those in IRs. We found a 2.3-fold increase of oligonucleotide repeats in P. scandens when compared with A. huixtlense, whereas amino acid frequency and codon usage revealed similarities. The ratio of transition to transversion mutations was 2.26 in P. scandens and 2.12 in A. huixtlense. Transversion mutations mostly translated in non-synonymous substitutions. The phylogenetic inference of the limited species showed the monophyly of the Araceae subfamilies. Our study provides insight into the molecular evolution of chloroplast genomes in the subfamily Pothoideae and family Araceae.

Comparison of Chloroplast Genomes among Species of Unisexual and Bisexual Clades of the Monocot Family Araceae

The chloroplast genome provides insight into the evolution of plant species. We de novo assembled and annotated chloroplast genomes of four genera representing three subfamilies of Araceae: Lasia spinosa (Lasioideae), Stylochaeton bogneri, Zamioculcas zamiifolia (Zamioculcadoideae), and Orontium aquaticum (Orontioideae), and performed comparative genomics using these chloroplast genomes. The sizes of the chloroplast genomes ranged from 163,770 bp to 169,982 bp. These genomes comprise 113 unique genes, including 79 protein-coding, 4 rRNA, and 30 tRNA genes. Among these genes, 17-18 genes are duplicated in the inverted repeat (IR) regions, comprising 6-7 protein-coding (including trans-splicing gene rps12), 4 rRNA, and 7 tRNA genes. The total number of genes ranged between 130 and 131. The infA gene was found to be a pseudogene in all four genomes reported here. These genomes exhibited high similarities in codon usage, amino acid frequency, RNA editing sites, and microsatellites. The oligonucleotide repeats and junctions JSB (IRb/SSC) and JSA (SSC/IRa) were highly variable among the genomes. The patterns of IR contraction and expansion were shown to be homoplasious, and therefore unsuitable for phylogenetic analyses. Signatures of positive selection were seen in three genes in S. bogneri, including ycf2, clpP, and rpl36. This study is a valuable addition to the evolutionary history of chloroplast genome structure in Araceae.

Molecular evolution of chloroplast genomes in Monsteroideae (Araceae)

This study provides broad insight into the chloroplast genomes of the subfamily Monsteroideae. The identified polymorphic regions may be suitable for designing unique and robust molecular markers for phylogenetic inference. Monsteroideae is the third largest subfamily (comprises 369 species) and one of the early diverging lineages of the monocot plant family Araceae. The phylogeny of this important subfamily is not well resolved at the species level due to scarcity of genomic resources and suitable molecular markers. Here, we report annotated chloroplast genome sequences of four Monsteroideae species: Spathiphyllum patulinervum, Stenospermation multiovulatum, Monstera adansonii, and Rhaphidophora amplissima. The quadripartite chloroplast genomes (size range 163,335-164,751 bp) consist of a pair of inverted repeats (25,270-25,931 bp), separating a small single copy region (21,448-22,346 bp) from a large single copy region (89,714-91,841 bp). The genomes contain 114 unique genes, including four rRNA genes, 80 protein-coding genes, and 30 tRNA genes. Gene features, amino acid frequencies, codon usage, GC contents, oligonucleotide repeats, and inverted repeats dynamics exhibit similarities among the four genomes. Higher rate of synonymous substitutions was observed as compared to non-synonymous substitutions in 76 protein-coding genes. Positive selection was observed in seven protein-coding genes, including psbK, ndhK, ndhD, rbcL, accD, rps8, and ycf2. Our included species of Araceae showed the monophyly in Monsteroideae and other subfamilies. We report 30 suitable polymorphic regions. The polymorphic regions identified here might be suitable for designing unique and robust markers for inferring the phylogeny and phylogeography among closely related species within the genus Spathiphyllum and among distantly related species within the subfamily Monsteroideae. The chloroplast genomes presented here are a valuable contribution towards understanding the molecular evolutionary dynamics in the family Araceae.

Evolutionary dynamics of chloroplast genomes in subfamily Aroideae (Araceae)

Aroideae is the largest and most diverse subfamily of the plant family Araceae. Despite its agricultural and horticultural importance, the genomic resources are sparse for this subfamily. Here, we report de novo assembled and fully annotated chloroplast genomes of 13 Aroideae species. The quadripartite chloroplast genomes (size range of 158,177-170,037 bp) are comprised of a large single copy (LSC; 75,594-94,702 bp), a small single copy (SSC; 12,903-23,981 bp) and a pair of inverted repeats (IRs; 25,266-34,840 bp). Notable gene rearrangements and IRs contraction / expansions were found for Anchomanes hookeri and Zantedeschia aethiopica. Codon usage, amino acid frequencies, oligonucleotide repeats, GC contents, and gene features revealed similarities among the 13 species. The number of oligonucleotide repeats was uncorrelated with genome size or phylogenetic position of the species. Phylogenetic analyses corroborated the monophyly of Aroideae but were unable to resolve the positions of Calla and Schismatoglottis.

Comparison of Whole Plastome Sequences between Thermogenic Skunk Cabbage Symplocarpus renifolius and Nonthermogenic S. nipponicus (Orontioideae; Araceae) in East Asia

Symplocarpus, a skunk cabbage genus, includes two sister groups, which are drastically different in life history traits and thermogenesis, as follows: The nonthermogenic summer flowering S. nipponicus and thermogenic early spring flowering S. renifolius. Although the molecular basis of thermogenesis and complete chloroplast genome (plastome) of thermogenic S. renifolius have been well characterized, very little is known for that of S. nipponicus. We sequenced the complete plastomes of S. nipponicus sampled from Japan and Korea and compared them with that of S. renifolius sampled from Korea. The nonthermogenic S. nipponicus plastomes from Japan and Korea had 158,322 and 158,508 base pairs, respectively, which were slightly shorter than the thermogenic plastome of S. renifolius. No structural or content rearrangements between the species pairs were found. Six highly variable noncoding regions (psbC/trnS, petA/psbJ, trnS/trnG, trnC/petN, ycf4/cemA, and rpl3/rpl22) were identified between S. nipponicus and S. renifolius and 14 hot-spot regions were also identified at the subfamily level. We found a similar total number of SSR (simple sequence repeat) motifs in two accessions of S. nipponicus sampled from Japan and Korea. Phylogenetic analysis supported the basal position of subfamily Orontioideae and the monophyly of genus Symplocarpus, and also revealed an unexpected evolutionary relationship between S. nipponicus and S. renifolius.