Phylogenetic analysis of the Critically Endangered Aquilaria khasiana (Thymelaeaceae) using barcode markers and chloroplast genome, with updated conservation status.

The species of Aquilaria and Gyrinops are renowned for being the primary sources of Agarwood, a valued resin, produced by these trees in response to fungal infections or physical damage. The major derivatives of Agarwood are wood chips and oil which are used in perfumes, incenses, cosmetics, and medicines. Due to high international trade and exploitation in the wild, the members of both genera are listed under Appendix II of the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES). Aquilaria khasiana, endemic to the Indian state of Meghalaya, is a less-studied CITES-listed species. The present study reveals its occurrence in an additional location i.e., in Jeypore Reserve Forest, Assam. The species identity was confirmed using morphological and barcode markers (ITS2, rbcl, and matK). The chloroplast genome was sequenced for the first time to explore plastome characteristics and reconstruct well-resolved phylogeny. Additionally, its conservation status assessment was carried out considering its new distributional records. Phylogenetic analyses, based on chloroplast genome data and the three barcode markers showed that both Aquilaria and Gyrinops are paraphyletic, with some species of Aquilaria nested within the Gyrinops clade. Despite possessing distinct morphological traits of Aquilaria, A. khasiana cluster with the Gyrinops along with the only Indian Gyrinops species, viz. G. walla as in the case of all previous phylogenetic analyses. Based on the present and previous molecular studies, it is concluded that Gyrinops is paraphyletic to Aquilaria. The chloroplast genome contained 90 protein-coding genes, 38 tRNAs, and 8 rRNAs. The present conservation status assessment supports retaining the species as Critically Endangered but with modified IUCN criteria and subcriteria.