A repeated sequencing of the chloroplast genome of Bletilla striata (Orchidaceae) and its taxonomic implications

Bletilla plants are well-known herbs in China with various medicinal properties and applications. The species of the genus are morphologically similar and often misidentified during the practice process. Comprehensive genetic information is thus essential for understanding the taxonomy and evolution of the genus. In this study, the chloroplast genome of a selected lineage of Bletilla striata was sequenced and phylogenetically analysed. The sequenced genome was 159499 bp in length, displaying a quadripartite structure consisting of a large single copy (LSC) region, a small single copy (SSC) region, and two inverted repeat (IR) regions. It contained 135 unique genes, of which 89 were protein-coding genes, 38 tRNA genes, and 8 rRNA genes. Several 9-10bp indels and an 8bp disparity in length were observed between the genome and a previously reported B. striata genome with accession number MT193723. This might represent the normal intra-population genetic variation within the B. striata species. A phylogenetic reconstruction involving 20 Epidendroideae species placed the newly sequenced lineage of B. striata within a major Bletilla clade containing B. ochracea and B. formosana, a sister group to the genus Thunia. In contrast, B. sinensis was positioned within a separate clade, distant from the major Bletilla clade. The distribution pattern and the possible gene flow within the genus Bletilla indicated that the species B. striata, B. ochracea, and B. formosana shared a closer affiliation with each other than with B. sinensis. Nevertheless, whether or not the species B. sinensis should be reclassified as a member of the genus Mengzia required further field investigation and morphological evidence, as well as additional molecular data.