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Mid-Miocene divergence of Ionopsidium and Cochlearia and its impact on the systematics and biogeography of the tribe Cochlearieae (Brassicaceae)

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Abstract:

Tribe Cochlearieae is among few isolated evolutionary lineages in the mustard family and comprises only about 30 species. Earlier taxonomic concepts recognised five genera that might belong with Cochlearia in this tribe (Bivonaea, Ionopsidium, Minaea, Pastorea, Thlaspi), though Pastorea and Minaea have already been reduced to synonymy of Ionopsidium. Focusing on DNA sequence information from the nuclear-encoded internal transcribed spacer regions ITS1 and ITS2 and the plastid trnL-F region, the phylogenetic position of all Ionopsidium species is evaluated within a detailed phylogenetic framework of tribe Cochlearieae. It is shown that the tribe can be divided into two major groups: (i) a central European Cochlearia clade extending its distribution far into northern and arctic regions, and (ii) a western Mediterranean clade comprising all six Ionopsidium species and three Cochlearia species from the Iberian Peninsula nested within Ionopsidium. Consequently, neither Cochlearia nor Ionopsidium represent monophyletic genera. The deep split between the two clades dates back to the middle Miocene, approximately 13.8 million years ago. The divergence times between the different major groups within the Ionopsidium clades predate or are associated with the Messinian salinity crisis in the late Miocene which also agrees with the relictual and phylogenetically isolated status of the tribe. Only taxa of Cochlearia sect. Cochlearia (Cochlearia clade) underwent a rapid and very recent radiation in the mid or late Pleistocene. Four new taxonomic combinations (Ionopsidium aragonensis (H.J. Coste & SouliƩ) M. Koch, I. aragonensis subsp. navarranum (P. Monts.) M. Koch, I. glastifolium (L.) M. Koch, and I. megalospermum (Maire) M. Koch) and the new tribe Bivonaeeae are proposed to reflect the deep evolutionary split within the group, which is further supported by DNA sequence variation of the nuclear-encoded, single-copy gene chalcone synthase (chs).

Keywords: BIOGEOGRAPHY; BIVONAEA; BIVONAEEAE; BRASSICACEAE; COCHLEARIA; COCHLEARIEAE; IONOPSIDIUM; MEDITERRANEAN; MIOCENE

Document Type: Research Article

Affiliations: Department of Biodiversity and Plant Systematics, Im Neuenheimer Feld 345, Centre for Organismal Studies (COS) Heidelberg, Heidelberg University, 69120 Heidelberg, Germany;, Email: marcus.koch@cos.uni-heidelberg.de

Publication date: February 21, 2012

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