Pollen morphology of the Swertiinae (Gentianaceae): phylogenetic implications

Abstract

Recent molecular surveys of the Swertiinae (Gentianaceae–Gentianeae) revealed unexpected phylogenetic relationships, including polyphyly of the genera Gentianella, Jaeschkea, Lomatogonium and Swertia. To find new non-molecular characters supporting the phylogeny, we examined the exine variation of 73 species of all major lineages of subtribe Swertiinae using environmental scanning electron miscroscopy supplementing older, mainly light microscopical, studies. In contrast to previous studies, we were able to pick out taxa from phylogenetic key positions with particular focus on Swertia. Many distantly related taxa such as parts of Frasera, Gentianopsis, Halenia, Gentianella, Megacodon and several lineages of Swertia share a striate–reticulate or reticulate exine pattern. This is interpreted as the plesiomorphic character state of Swertiinae. There is also considerable variation of derived patterns; for example, different types of microechinate or almost smooth pollen was repeatedly observed in distantly related groups. Another extreme was the ring-shaped reticulation found in a North American species of Gentianopsis. Unfortunately, major relationships as revealed by molecular analyses were rarely supported because of the abundance of the plesiomorphic type and homoplasy even on low taxonomic levels; for example, within Lomatogonium. Exine variation was particularly useful in characterizing independent lineages of Swertia. For example, according to pollen characters and in agreement with other data, the Asian Swertia cuneata is a sister group of a strongly diversified African lineage and Swertia yunnanensis, which is rather aberrant in flower morphology, seems close to parts of Lomatogonium. © 2008 The Linnean Society of London, Botanical Journal of the Linnean Society, 2008, 157, 323–341.