PHYLOGENETIC IMPLICATIONS OF POLLEN MORPHOLOGY IN TRIBE AJUGEAE (LABIATAE)

A palynological survey of tribe Ajugeae (Labiatae) reveals an exceptional amount of variation in an otherwise rather stenopalynous family. Five pollen types are distinguished based on differences in colpal structure (operculate vs. inoperculate), supratectal sculpturing, and the structure of the columellate stratum. Only one of these pollen types occurs elsewhere in the Labiatae, but four of them can be found in the Verbenaceae. Particularly close resemblances in pollen morphology were noted among the members of the following sets of taxa (in Ajugeae unless otherwise noted: SC, Scutellarieae; VE, Verbenaceae): Amethystea, Rubiteucris, Schnabelia, Tetraclea, Trichostema, and many Verbenaceae (mostly Clerodendreae); Kinostemon, Teucrium, Teucridium (VE), Spartothamnella (VE), Oncinocalyx (VE), and Monochilus (VE); Holocheila, Renschia, Tinnea, and Scutellaria (SC). The distribution of derived pollen features (hypothesized to be synapomorphies) suggests that tribe Ajugeae and the family Labiatae are polyphyletic. The segregation of Rubiteucris and Holocheila from Teucrium is supported by pollen morphology, but Kinostemon should be retained within Teucrium.