Molecular phylogenetics of Cochlearia (Brassicaceae) and allied genera based on nuclear ribosomal ITS DNA sequence analysis contradict traditional concepts of their evolutionary relationship

Abstract

The systematics and phylogeny of the genus Cochlearia and allied genera are unsettled. There are no clearly defined genera and subtribal structures to determine subtribe Cochleariinae in respect to subtribe Thlaspidinae. The use of morphological data, such as fruit form or embryo characters have resulted in contradictory taxonomic concepts in the past due to their homoplastic nature. We investigated all sections of genus Cochlearia recognised in the most common concepts, as well as some genera such as Ionopsidium, Bivonaea, Pastorea and Thlaspi s. 1. pro parte. Previous studies based on molecular data and morphological studies have shown close relationships between taxa from subtribe Cochleariinae and Thlaspidinae. The Internal Transcribed Spacer regions of the nuclear encoded ribosomal DNA operon and the plastidic trnL intron were sequenced from a number of genera. A molecular phylogeny was derived and compared to traditional classification systems. These data grouped sections of Cochlearia outside the Cochlearia/Ionopsidium core group and integrated them either closely to genus Noccaea in subtribe Thlaspidinae (sect. Pseudosempervivum) or positioned them outside both the Cochlearia core group and the Thlaspi s. 1. clade (sect. Hilliella). The molecular data indicate that subtribal arrangements in tribe Lepidieae are artificial and do not reflect evolutionary history. The genus Cochlearia is represented by sections Cochlearia and Glaucocochlearia and the genus Ionopsidium should be integrated into Cochlearia.