Plastomes of Ten Blumea Species (Asteraceae): Comparative Analysis and Phylogenetic Relationships.

Blumea (Asteraceae) comprises about 100 species distributed across tropical Asia, Africa, and Australia, many of which have medicinal value. However, morphological variation caused by hybridization has left the taxonomy of this genus unresolved. In this study, we assembled the chloroplast genomes of six Blumea species (B. repanda, B. axillaris, B. sinuata, B. martiniana, B. megacephala, and B. formosana) and compared them with those of four published species (B. oxyodonta, B. tenella, B. aromatica, and B. balsamifera). The six new plastomes are similar in size (150,783-151,281 bp), with a typical quadripartite structure, each containing 131 genes (86 protein-coding genes, 37 tRNAs, and 8 rRNAs). Comparative analyses revealed conserved genome architecture, stable IR/SC boundaries, and no rearrangements. Six non-coding and four coding regions were identified as candidate DNA barcodes. A total of 395 dispersed repeats, 79 tandem repeats, and 547 SSRs were identified. Among the 59 preferred codons, 29 were high-frequency (RSCU > 1), and 28 of these ended in A/U. Additionally, positive selection was detected in 21 genes, for example, ycf1, ycf2, rpoB, and ndhA. Phylogenetic analyses (ML and BI) based on 23 taxa (21 Inuleae species plus two outgroups) showed that Blumea is a highly supported monophyletic group (BS = 100%, PP = 1.00), internally divided into three subclades: subclade I (B. axillaris, B. oxyodonta, B. megacephala, B. repanda, B. sinuata, and B. tenella), subclade II (B. balsamifera), and subclade III (B. aromatica, B. formosana, and B. martiniana), with the latter three species all belonging to Section Macrophylla. These genomic resources lay a foundation for future phylogenetic, population-genetic, and biotechnological studies of Blumea.