Phylogeny and character evolution in subfamily Nepetoideae (Labiatae)

The purpose of this research is to contribute toward a phylogenetic and hence more predictive classification of subfamily Nepetoideae (Labiatae). The study addresses the following specific questions: (1) Is subfamily Nepetoideae monophyletic? Can monophyletic subgroups be delineated? (3) Are the inferred phylogenetic relationships concordant with the existing classifications? (3) What are implications of the inferred phylogeny for interpreting character evolution and biogeography?Phylogenetic relationships were inferred by parsimony analysis of chloroplast DNA restriction site variation. The study group included 58 genera of Labiatae, representing all tribes recognized in Bentham's (1876) classification, and tobacco as a distant outgroup. Floral characters were studied on live specimens maintained in the Ohio University Botanical Garden, complemented by herbarium material. Pollen from 128 species in 69 genera of subfamily Nepetoideae was studied using SEM. The cpDNA-based phylogeny was used to interpret floral evolution and biogeography in the subfamily.Parsimony analysis of cpDNA restriction site variation supports monophyly of subfamily Nepetoideae and suggests that its sister group is a member of the Verbenaceae. The inferred phylogeny is more concordant with Wunderlich's (1967) classification than those of Bentham (1876) or Briquet (1895-97). Other notable systematic findings are: (1) the inclusion of Catoferia, Lavandula and Tetradenia in tribe Ocimeae (2) the recognition of a close relationship between Elsholtzia, Collinsonia and Perilla and (3) the recognition that Salvia is closely related to Dorystoechas, Perovskia, Rosmarinus and Lepechinia, but not to Blephilia, Monarda or Ziziphora.Ascending stamens are ancestral in subfamily Nepetoideae, declinate stamens have evolved in three lineages and spreading stamens in at least six lineages. Psilate pollen is derived and has evolved from suprareticulate pollen in at least five lineages of subfamily Nepetoideae. Two mechanisms are proposed: (1) reduction in the height of the supratectal ridges and (2) disintegration of the tectum resulting in pollen with a semitectate structure. Subfamily Nepetoideae originated in Eurasia with subsequent migration of several lineages into the New World.