SYSTEMATIC IMPLICATIONS OF POLLEN MORPHOLOGY IN TRIBE PROSTANTHEREAE (LABIATAE)

A palynological survey of Tribe Prostanthereae (Labiatae) reveals that the pollen is tricolpate or 6- (8) colpate, tectate-perforate to reticulate, with or without spinulose sculpturing; the columellae are simple and the colpal membranes bear sexine elements. Three sculpturing variants are distinguishable. None of the pollen types in the Prostanthereae have been observed elsewhere in the Labiatae s. str., but the one hypothesized to be ancestral in the tribe (tricolpate, microreticulate, lacking spinules) is widespread in the Labiatae s.l. (i.e., including many genera traditionally assigned to Verbenaceae). The two sections of Prostanthera differ in pollen size and number of colpi, providing a probable synapomorphy for sect. Klanderia (6-colpate pollen) and phenetic support for its segregation as a distinct genus (Cryphia). Conn's placement of Eichlerago in synonymy with Prostanthera is supported by their similar pollen morphology. The distribution of spinulose sculpturing (a derived state) suggests that Prostanthera, Wrixonia, and perhaps Hemiandra form a clade within the tribe, but the inclusion of Hemiandra conflicts with floral characters. The hypothesis that tribe Prostanthereae is closely related to subfam. Chloanthoideae sensu Briquet (the latter variably assigned to Verbenaceae s.l., Labiatae s.l., or its own family) is more consistent with pollen morphology than the traditional placement of the tribe within the Labiatae s. str.