A phylogenetic analysis of the Illiciaceae based on sequences of internal transcribed spacers (ITS) of nuclear ribosomal DNA

Abstract

Sequences of the internal transcribed spacers (ITS) of nuclear ribosomal DNA were determined for 15 species of Illicium (Illiciaceae) to examine phylogenetic relationships. The ITS trees show a major dichotomy between the two North American species (I. floridanum and I. parviflorum) and the remaining east Asian species. This suggests that the existing division between two sections (sect. Illicium and sect. Cymbostemon) of Illicium based on tepal characters is unnatural. The ITS phylogeny shows congruence with palynology: of the species examined, the three species (I. angustisepalum, I. anisatum and I. fargesii) from sect. Illicium that possess trizonocolpate pollen consistently form a clade, although nesting within a clade consisting of the species of sect. Cymbostemon, which generally have trisyncolpate pollen. The low ITS sequence divergence and the close relationship among east Asian species suggest a recent diversification of this group of species or an unusual slowdown of sequence mutations.