Diversity and biogeography of N i‐hyperaccumulators of A lyssum section O dontarrhena ( B rassicaceae) in the central western M editerranean: evidence from karyology, morphology and DNA sequence data

The diversity of A lyssum section O dontarrhena in the central–western M editerranean region was investigated to elucidate relationships and biogeography of N i‐hyperaccumulators in the group. Karyological, morphometric and molecular phylogenetic analyses were performed on accessions of N i‐hyperaccumulators from serpentine outcrops and non‐hyperaccumulators from calcareous–dolomitic soils in the region. Alpine and A pennine populations of A . argenteum , S ardinian A . tavolarae and some T uscan A . bertolonii had a tetraploid chromosome complement and larger silicles, seeds and seed wings than diploid accessions. DNA sequences from the plastid rpo C 1 locus corroborated the monophyly of section O dontarrhena but species relationships were poorly resolved. B ayesian analysis of combined ITS ‐ rpo C 1 sequences retrieved three main lineages including hyperaccumulators and non‐hyperaccumulators of contrasting geographical origin. One lineage was mainly continental and included alpine and northern A pennine populations of A . argenteum , the B alkan complex of A . murale and the I berian group of A . serpyllifolium , sister to C orsican A . robertianum as suggested by their similar diploid karyotype. In this clade no divergence was found between typical A . serpyllifolium and related N i‐hyperaccumulator races from the I berian peninsula, supporting their conspecific status. A second lineage was prevalently M editerranean and included the sister species A . bertolonii and A . tavolarae , and other endemics from S icily, the southern B alkans and T urkey from dolomite and serpentine habitats. The present data suggest new model systems consisting of hyperaccumulators and non‐hyperaccumulators of proven phylogenetic affinity for further research on the molecular mechanisms of N i‐hyperaccumulation and serpentine tolerance at the diploid and tetraploid level. © 2013 The Linnean Society of London, Botanical Journal of the Linnean Society , 2013, 173 , 269–289.