Phylogeny of the Genus Noccaea (Brassicaceae) and a Critical Review of its Generic Circumscription

Abstract

Noccaea Moench is taxonomically one of the most problematic genera of the Brassicaceae. The radical revision of Thlaspi L. s.l. by Meyer in 1973 (Meyer, 1973) split it into 12 segregate genera, including Noccaea, but subsequent molecular studies suggested that this complex includes at least four unrelated genera (Thlaspi s. str., Mummenhoffia Esmailbegi & Al-Shehbaz, Noccidium F. K. Mey., and Noccaea). Although several taxonomic treatments have since been proposed to sort out the systematic problems of Noccaea, debates are still ongoing. Some authors have argued that all segregates of Thlaspi should be considered as independent but related genera, whereas others recognize them as synonyms of a large and polymorphic Noccaea. In this study, we present the first extensively sampled phylogenetic analysis of tribe Coluteocarpeae (Thlaspi segregates including Noccaea) using internal transcribed spacer (ITS) DNA sequences from 92 of the ca. 130 species (70%) in the tribe (39 studied here for the first time) and plastidic trnL-F regions from 73 species (42 studied here for the first time), representing the full range of morphological variation and geographical distribution. All main clades are discussed in detail, and the taxonomic status of all Thlaspi s.l. segregates is evaluated against recent taxonomic treatments. In particular, the tribal placement of Noccidium is changed to Coluteocarpeae, and the genus Pseudosempervivum (Boiss.) Grossh. is reduced to synonymy of Noccaea. The new name N. mummenhoffiana Özüdoğru & Al-Shehbaz and the new combinations N. aucheri (Boiss.) Özüdoğru & Al-Shehbaz and N. sempervivum (Boiss. & Balansa) Özüdoğru & Al-Shehbaz are proposed.