Internal Transcribed Spacer Sequence Phylogeny ofCrambeL. (Brassicaceae): Molecular Data Reveal Two Old World Disjunctions

Abstract

CrambeL. (Brassicaceae) is an Old World genus with a disjunct distribution among four major centers of species diversity. A phylogenetic analysis of nucleotide sequences of the internal transcribed spacers (ITS) of the nuclear ribosomal repeat was conducted with 27 species ofCrambeand 18 related genera. Cladistic analyses using weighted and unweighted parsimony supportCrambeas a monophyletic genus with three major lineages. The first comprises those taxa endemic to the Macaronesian archipelagos. Taxa with a predominant Mediterranean distribution form the second assemblage, and a disjunction between east Africa (C. abyssinica) and the Mediterranean (C. hispanica) occurs in this clade. The third lineage includes all Eurosiberian–Asian taxa andC. kilimandscharica,a species from the highlands of east Africa. A basal biogeographic split between east Africa and Eurasia is present in the third clade. The patterns of relationships in the ITS tree are concordant with known climatic events in northern Africa and southwestern Asia since the middle Miocene. The ITS trees are congruent with the current sectional classification except for a few members of sectionsCrambe, Leptocrambe,andOrientecrambe(C. cordifolia, C. endentula, C. kilimandscharica,andC. kotschyana). Low levels of support in the basal branches do not allow resolution of which genera of the subtribes Raphaniae or Brassicinae are sister toCrambe.Both subtribes appear to be highly polyphyletic in the ITS trees.