Swertia shiraiwamontana (Gentianaceae), a New Species Previously Identified as S. bimaculata in Japan

Abstract

An unknown taxon morphologically similar to Swertia bimaculata (Sieb. & Zucc.) Hook.f. & Thoms. ex C.B.Clarke (Gentianaceae) was discovered in Japan. This taxon and S. bimaculata were found growing in close proximity or side by side at two surveyed sites. In this study, we examined the relationship between S. bimaculata and the unknown taxon using high-resolution molecular phylogenetic analyses and population genetic analysis, employing multiplexed ISSR genotyping by sequencing (MIG-seq). The results indicated that the unknown taxon forms a distinct clade, separate from S. bimaculata, with no evidence of genetic admixture. Detailed morphological observations revealed that it can be distinguished from S. bimaculata by the following characters: color of filaments, color and shape of nectaries, size of black purple spots on the adaxial corolla surface, color of the abaxial corolla surface, and posture of corolla lobes after anthesis. Based on these findings, we formally describe it as a new species, S. shiraiwamontana Myotoishi & Yahara.