Molecular systematics of the Brassicaceae: evidence from coding plastidic <i>matK</i> and nuclear <i>Chs</i> sequences

TLDR

Phylogenetic relationships were inferred using nucleotide sequence variation of the nuclear‑encoded chalcone synthase gene (Chs) and the chloroplast gene matK for members of five tribes from the family Brassicaceae to analyze tribal and subtribal structures. The combined matK‑Chs analysis largely agrees with individual gene trees but provides higher resolution and support for deeper branches, revealing that Lepidieae, Arabideae, and Sisymbrieae are not monophyletic, that Arabideae and Lepidieae contain four interspersed lineages, that Brassiceae may be the sole monophyletic traditional tribe, and estimating divergence times of 5.8 Myr for the Arabidopsis–Cardaminopsis split, 20 Myr for Brassica–Arabidopsis, and ~40 Myr for the deepest crucifer split.

Abstract

Phylogenetic relationships were inferred using nucleotide sequence variation of the nuclear‐encoded chalcone synthase gene ( Chs ) and the chloroplast gene matK for members of five tribes from the family Brassicaceae to analyze tribal and subtribal structures. Phylogenetic trees from individual data sets are mostly in congruence with the results from a combined matK‐Chs analysis with a total of 2721 base pairs, but with greater resolution and higher statistical support for deeper branching patterns. The analysis indicates that tribes Lepidieae, Arabideae, and Sisymbrieae are not monophyletic. Among taxa under study four different lineages each were detected in tribes Arabideae and Lepidieae, interspersed with taxa from tribes Sisymbrieae, Hesperideae, and Brassiceae. It is concluded that tribe Brassiceae might be the only monophyletic group of the traditional tribes. From our data we estimated several divergence times for different lineages among cruciferous plants: 5.8 mya (million years ago) for the Arabidopsis – Cardaminopsis split, 20 mya for the Brassica – Arabidopsis split, and ∼40 mya for the age of the deepest split between the most basal crucifer Aethionema and remaining cruciferous taxa.