A search for pollen morphological synapomorphies to classify rogue genera in Compositae (Asteraceae)

Abstract

Focusing on Compositae, this paper highlights and exemplifies the range of questions to which pollen morphology may contribute in the investigation of problematic taxa. Using a literature survey and new palynological data from LM and SEM studies, the pollen of a number of “rogue genera” was described and compared with that of potential related taxa in Compositae. Rogue genera are defined as taxa that have traditionally been difficult to classify, usually having highly divergent macro-morphological characters compared to the rest of Compositae. They include genera of known tribe but unknown position within that tribe and genera or small tribes of uncertain position in Compositae, as well as taxa that have recently been placed using molecular data but whose morphology continues to intrigue synantherologists. In the majority of cases, palynology was found to provide new sets of characters which could be compared to the robust hypothesis of relationships shown in the recent DNA-based supertree. Pollen variously provided support and diagnostic characters for some groups (e.g. Hesperomannia, Hoplophyllum, Eremothamnus, Tarchonantheae, Corymbieae and Gymnarrheneae), suggested some possible affinities for taxa currently excluded from phylogenetic studies using DNA (such as Moquinia, Catananche, Pacourina and Platycarpha), or to some degree contradicted existing phylogenies (e.g. Gundelia and Warionia), suggesting areas for future research.