Salvia is the largest genus within Lamiaceae, with about 980 species currently recognized. East Asia, with approx. 100 species, is one of the three major biodiversity centres of Salvia. However, relationships within this lineage remain unclear, and the staminal lever mechanism, which may represent a key innovation within the genus, has been understudied. By using six genetic markers and nearly comprehensive taxon sampling, this study attempts to elucidate relationships and examine evolutionary trends of staminal development within the East Asia (EA) Salvia clade.
Ninety-one taxa of EA Salvia were sampled and 34 taxa representing all other major lineages of Salvia were included for analysis. Two nuclear [internal transcribed spacer (ITS) and external transcribed spacer (ETS)] and four chloroplast (psbA–trnH, ycf1–rps15, trnL–trnFand rbcL) DNA markers were used for phylogenetic analysis employing maximum parsimony (MP), maximum likelihood (ML) and BEAST, with the latter also used to estimate divergence times.
All Salvia species native to East Asia form a clade, and eight major subclades (A–G) were recognized. Subclade A, comprising two limestone endemics (S. sonchifolia and S. petrophila), is sister to the remainder of EA Salvia. Six distinct stamen types were observed within the EA clade. Stamen type A, with two fully fertile posterior thecae, only occurs in S. sonchifolia and may represent the ancestral stamen type within EA Salvia. Divergence time estimates showed that the crown of EA Salvia began to diversify approx. 17.4 million years ago.
This study supports the adoption of a broadly defined Salvia and treats EA Salvia as a subgenus, Glutinaria, recognizing eight sections within this subgenus. Stamen type A is ostensibly plesiomorphic within EA Salvia, and the other five types may have been derived from it. Staminal morphology has evolved in parallel within the EA Salvia, and staminal structure alone is inadequate to delimit infrageneric categories.