Calanthe is the largest genus in tribe Collabieae (Epidendroideae, Orchidaceae) that is distributed in Asia and Africa. Its species have numerous ornamental and medicinal values. However, due to the uncertainties in the precise delimitation characters and the incongruent molecular phylogeny within the Calanthe alliance, its taxonomic classifcation has not been sufficiently resolved.

Researchers from the Eastern African Plant Flora and Taxonomy Research Group of Wuhan Botanical Garden sequenced, assembled and annotated the complete chloroplast genome of eight species from two genera in the Calanthe alliance: Calanthe and Phaius. Phylogenetic relationships in the Calanthe group were resolved.

Results from this study indicated that the complete plastomes of the Calanthe group species have a quadripartite structure that varied in size ranging between 150,105bp and 158,714bp. The plastome can be divided into four regions, consisting of a large single-copy region (83,364bp- 87,450bp), a small single-copy region (16,297bp -18,586bp), and a pair of inverted repeat regions (25,222bp - 26,430bp).

The plastomes encoded 131-134 differential genes, consisted of 85-88 protein-coding genes, 37-38 tRNA genes, and 8 rRNA genes. Comparative analysis showed no definitive rearrangements or gene inversions were recorded, indicating that the Calanthe group plastome was highly conserved. However, three genes(ndhC, ndhF, and ndhK. ) were lost in P. delavayi.

Repeats were widespread in the non-coding regions compared to the coding regions, hence important for species DNA barcoding. Phylogenetic analysis revealed that the genus Calanthe formed a high support clade as a paraphyletic group, and confirmed the position of Phaius delavayi in the genus Calanthe as opposed to its previous placement in Phaius.

In this study, the complete chloroplast genemo of eight Calanthe group species are sequenced and compared. These results are valuable genetic resources and a basis for studying evolutionary relationships and population genetics among orchid species.

The research titled “Plastome structure of 8Calanthes.l. species (Orchidaceae): Comparative Genomics, Phylogenetic Analysis” was published in the international journal of BMC Plant Biology. This work was supported by grants from International Partnership Program of Chinese Academy of Sciences, the National Natural Science Foundation of China, Special Project of Orchid Survey of National Forestry and Grassland Administration, and Sino-Africa Joint Research Center, CAS.

A Kenyan student, Consolata Nanjala, is the first author. Professor HU Guangwan is the corresponding author. Several students from the group take part in this study.