Viburnum japonicum (Thunb.) Sprengel is an endangered species endemic to coastal regions of eastern Asia (China, Japan, and South Korea). However, its systematic position has been controversial. In this study, we present the complete chloroplast (cp) genome of V. japonicum (GenBank OP644292) sequenced using the Illumina NovaSeq platform. The cp genome has a total length of 158,606 bp and a G+C contents of 38.08%. It consists of a large single-copy (LSC) region, a small single-copy (SSC) region, and a pair of inverted repeats (IRs) regions measuring 87,060 bp, 18,510 bp, and 26,516 bp, respectively. A total of 131 genes were identified, including 87 protein-coding genes, 36 transfer RNA genes (tRNAs), and 8 ribosomal RNA genes(rRNAs). Additionally, a total of 44 dispersed repeats were detected, including three types: forward, palindromic, and reverse. Among the 38 SSR loci that were discovered, the majority were mononucleotide loci composed of A/T. Furthermore, we found that 15 genes (accD, atpF, ndhA, ndhB, petB, petD, rpl16, rpl2, rpoC1, rps12, rps16, trnA-UGC, trnI, trnK-UUU, and trnL-UAA) contain one intron, while clpP and ycf3 have two introns. The relative synonymous codon usage (RSCU) analysis detected 31 high-frequency codons, where A/U bases accounted for 93.55% of the total, indicating an asymmetry in chloroplast gene and a presence for A/U bases. Comparative analysis of genome structure and sequences data of V. japonicum chloroplast genomes in comparison with other closely related species demonstrated a high level of conservation in their structure and organization. Furthermore, three mutation hotspots (psbH, rps19, and trnL) were identified, which could be valuable for future phylogenetic and population genetic research. Phylogenetic analysis revealed that the two accessions of V. japonicum are closely related to a group of V. setigerum, V. erosum, and V. fordiae within the Viburnum genus. In conclusion, this study provides important insights for accurately identifying and understanding the phylogeny of Viburnum species through the complete cp genome sequencing of V. japonicum.

The mitochondrial genome of Spartina alterniflora, an invasive species with significant ecological and economic impacts, was analyzed to provide a theoretical basis for understanding its phylogenetic relationships and molecular biology. Mitochondrial genome sequences of S. alterniflora and 23 related species from NCBI were utilized for bioinformatics and comparative genomic analyses. A sliding window analysis identified three genes (rps2, atp9, and nad6) as potential DNA barcodes for species identification. Intracellular gene transfer (IGT) events between mitochondrial and chloroplast genome were detected, highlighting the dynamic nature of genomic evolution. A selective pressure analysis revealed that most protein-coding genes (PCGs) underwent purifying selection (K_a/K_s < 1), while the nad2 and ccmB genes showed signs of positive selection pressure (K_a/K_s > 1), indicating their role in adaptation. A phylogenetic analysis demonstrated a close relationship between S. alterniflora and Eleusine indica, supported by a collinearity analysis, which suggests environmental convergence. This study provides novel insights into the structural and evolutionary characteristics of the S. alterniflora mitochondrial genome, offering valuable genomic resources for future research on invasive species management and evolutionary biology.

The genus Rhododendron presents significant challenges for systematic classification due to extensive hybridization and adaptive radiation. Here, we employed double-digest restriction site-associated DNA sequencing (ddRAD-seq) to resolve phylogenetic relationships among nine ecologically significant Rhododendron species (34 accessions) endemic to Zhejiang Province, China, a biodiversity hotspot for this genus. Using R. simsii as the reference genome, we generated 39.40 Gb of high-quality sequencing data with a Q30 score of 96.65% and a GC content of 39.63%, achieving an average alignment rate of 92.79%. Through stringent filtering (QD ≥ 2, MQ ≥ 40), we identified 14,048,702 genome-wide single nucleotide polymorphism (SNP), predominantly characterized by the mutation types T:A>C:G and C:G>T:A. The widespread R. simsii and R. simsii var. putuoense exhibited significant genetic diversity, whereas the low-altitude widespread R. molle and the endemic R. simiarum exhibited lower genetic diversity. Moderate genetic differentiation (F_st = 0.097) was observed between R. simsii and R. simsii var. putuoense, while substantial genetic differentiation was detected among the other Rhododendron species. Principal component analysis (PCA), combined with phylogenomic reconstruction, demonstrated that the Rhododendron genus can be stratified into six well-supported genetic clades. Furthermore, this study provides the first genomic validation of the sibling relationship between R. simsii and its variety, R. simsii var. putuoense, and clarifies the systematic position of R. huadingense, suggesting that it should be classified as a new subgenus. This study establishes ddRAD-seq as a cost-effective tool, providing both a theoretical framework for SNP-based phylogenetics and critical insights for conserving China’s azalea biodiversity.