Phylogeny of Campanulaceae S. Str. Inferred from Its Sequences of Nuclear Ribosomal DNA

Abstract

Ninety-three taxa comprising thirty-two genera (plus four outgroups from Lobeliaceae) were used to estimate a phylogeny of the Campanulaceae based on ITS sequences of nuclear ribosomal DNA. From 2629 most parsimonious trees, a strict consensus tree with bootstrap values was constructed, in addition to a phylogram showing branch lengths. The topologies of these two trees are discussed in relation to the pollen and capsule morphology within the family, in addition to chromosome number and geographical distribution. The results show that there is a major dichotomy between the colpate/colporate pollen alliance (platycodonoid taxa) and the porate pollen alliance (wahlenbergioid and campanuloid taxa). Both these major alliances are monophyletic. Within the porate alliance there are two major clades, the wahlenbergioids and the campanuloids. The campanuloid Glade is further subdivided into two major clades representing the Rapunculus and the Campanula s. str. groups of taxa, plus three smaller clades that are considered as transitional taxa. It is argued that the family originated in a fragmenting West Gondwanaland and that tectonic processes are responsible for the major dichotomy in the family. The colpate/colporate platycodonoids subsequently remained relatively relictual in Asia, whereas the porate taxa spread over much of the Northern and Southern Hemispheres. The campanuloid lineage spread over the Northern Hemisphere from a major evolutionary center in the Mediterranean region and is represented in North America only by the Rapunculus group. The wahlenbergioid lineage is widely dispersed across the southern continents and oceanic islands but has a major secondary center of diversification in southern Africa. The use of ITS provides insights for future investigations and a phylogenetic framework that can be tested with other data sets. Its limitations for phylogeny reconstruction are briefly discussed. More extensive taxon sampling and additional data sets are required to refine these results and for a new classification of the Campanulaceae to be proposed.