Nutlet micromorphology of Japanese Salvia (Salviinae, Lamiaceae) and its systematic significance

Salvia is a taxonomically challenging genus in the Japanese archipelago, comprising 12 distinct species, eight of which are endemic. In this study, the nutlet micromorphology of 19 taxa (species and varieties) assigned to the sections Glutinaria , Heterosphace , Notiosphace , and Sobiso was investigated using light and scanning electron microscopy. This study aimed to evaluate the systematic significance of nutlet morphology in Japanese Salvia . Nutlet size ranged from 0.64 × 0.45 mm in S. plebeia (sect. Notiosphace ) to 3.27 × 2.27 mm in S. koyamae (sect. Glutinaria ). The L/W ratio varied from 1.06 in S. glabrescens var. repens (sect. Glutinaria ) to 2.54 in S. pygmaea var. pygmaea (sect. Sobiso ). Nutlet shapes were elliptic, narrow-elliptic, and ellipsoidal in sect. Sobiso ; ovoid to obovoid and spherical in sect. Glutinaria ; and ovoid in both sect. Heterosphace and sect. Notiosphace . Abscission scar morphology varied among the sections, being squarish, triangular, irregular, or orbicular in sect. Sobiso ; irregular to orbicular in sect. Glutinaria ; orbicular in sect. Heterosphace ; and triangular in sect. Notiosphace . Four major types of surface sculpturing were recognized: colliculate with irregular surface cells in sect. Glutinaria ; reticulate with pentagonal to hexagonal cells in sect. Sobiso ; tuberculate with large rounded knobs in sect. Heterosphace ; and verrucate with small wart-like projections in sect. Notiosphace . Principal component analysis (PCA) based on taxon means demonstrated that nutlet size-related characters contributed most strongly to the observed variation among the studied taxa. Overall, the diversity of nutlet morphology highlights the diagnostic value of these characters for taxonomic identification at both the species and sectional levels within Japanese Salvia .