On the identity of Dracocephalum breviflorum (Lamiaceae, Nepetoideae)

Abstract

As currently circumscribed, the genus Dracocephalum Linnaeus (1753: 594) includes the traditionally defined Hyssopus Linnaeus (1753: 569) and Lallemantia Fischer & Meyer (1840: 52), making it the second largest genus in subtribe Nepetinae (Nepetoideae, Lamiaceae), consisting of ca. 80 species (Chen et al. 2022). Morphologically, the genus is most similar to Nepeta Linnaeus (1753: 570), but it can be easily distinguished from the latter by its calyces with a thickened sinus-like fold between the bases of adjacent calyx lobes (Li & Hedge 1994; Harley et al. 2004). There are approximately 40 species of Dracocephalum distributed in China, of which 19 are endemic (Li & Hedge 1994; Chen et al. 2021, 2022). Among those endemic species, Dracocephalum breviflorum Turrill (1922: 154) was described on the basis of a specimen collected from Mount Everest area, southern Xizang (Tibet), China (A.F.R. Wollaston 255, K000911317). In the protologue, Turrill (1922) thought D. breviflorum is most similar to D. heterophyllum Bentham (1835: 738) but emphasized that the calyx morphology of the species (i.e., remarkably short and more distinctly 2-lipped than any previously known species of Dracocephalum) is unique in Dracocephalum. During our taxonomic revision of Dracocephalum in the Pan-Himalayan region, we found that D. breviflorum does not have a thickened sinus-like fold between the base of the calyx lobes, indicating it should be a member of the genus Nepeta. Given the importance of types in solving taxonomical issues (Wagensommer et al. 2016; Akhil et al. 2022; Perrino et al. 2023), we carefully compared the type specimens of both D. breviflorum and Nepeta coerulescens Maximowicz (1881: 529) (Fig. 1). In addition, we carried out observations of plants in the field (Fig. 2). The results of our research on herbarium specimens and in the field demonstrated that D. breviflorum and N. coerulescens are conspecific, and here we synonymize Dracocephalum breviflorum under Nepeta coerulescens.