Rediscovery, identity, and conservation strategies of a critically endangered endemic plant, <em>Hedyotis quinquinervia</em> Thwaites (Rubiaceae) in Sri Lanka

Sri Lanka, a biodiversity hotspot in Asia, records 30 Hedyotis species of which 25 species and a variety are endemic. Among these 25 species, seven Hedyotis species were categorized as critically endangered (CR), and 13 as endangered (EN). During our field survey in 2014, an extremely attractive plant belonging to the genus Hedyotis was discovered from Mount Thotupola, Sri Lanka. The plant was tentatively identified as H. quinquinervia. For accurate species identification, morphological characters were compared with voucher specimens, and identification keys were also used. In addition, DNA barcoding using the sequence of the internal transcribed spacer region of the nuclear ribosomal DNA (rDNA-ITS) region was performed, followed by molecular phylogenetic analysis. A simple method to remove a thick cuticle layer on the leaves was employed to obtain a sufficient amount of DNA suitable for Polymerase Chain Reaction. A comparison with its protologue and type specimen along with molecular phylogenetic analysis confirmed that the unidentified plant was H. quinquinervia Thwaites. The National Red List of Sri Lanka (2020) had revised H. quinquinervia as a CR species upon the rediscovery confirmed after the lapse of a century. Habitat characteristics, ex situ and in situ conservation measures for H. quinquinervia, and general conservation strategies applicable to threatened heterostylous plants are also discussed.