Molecular and morphological evidence for a new species of Siphocranion (Lamiaceae) from the Sino-Vietnamese border

Siphocranion is an oligotypic genus of Lamiaceae, with two species mainly distributed in subtropical China and one of them found also in northeastern India, Myanmar, and Vietnam. Based on field investigation, morphological comparison, and molecular phylogenetic analyses, a new species of Siphocranion from the Sino-Vietnamese border is described as S. flavidum. Bayesian and maximum likelihood analyses on two nuclear ribosomal DNA regions and six plastid DNA regions reveal that S. flavidum is a distinct species in the genus and may be sister to the Glade formed by the remaining two species of Siphocranion. Morphologically, the new species differs from S. macranthum and S. nudipes in its strigose stem with dark purple spots, thick papery lamina, significantly larger calyx, pale yellow corolla with tube slightly saccate at anterior side of base.