Odontarrhena stridii (Brassicaceae), a new Nickel-hyperaccumulating species from mainland Greece

Odontarrhena is a taxonomically difficult genus of the tribe Alysseae, including a number of critical species complexes in the Balkan Peninsula. One of these is O. baldaccii, which was previously included in the inconsistent taxon Alyssum fallacinum but recently shown to be distinct from it. In this paper we analyzed the still uncertain taxonomic circumscription of O. baldaccii by a comparative analysis of the population from the type locality in Crete and other populations from mainland Greece, which were previously attributed to A. fallacinum or dubitatively included in O. baldaccii s.l. Results supported the separation of these mainland populations in a new distinct species, here described as Odontarrhena stridii. Plant habit, leaf shape and size and silicle shape were the major distinguishing morphological characters. Molecular data also suggested divergence between the two groups of populations, while supporting their phylogenetic affinity. The two species are diploid schizo-endemics with 2n = 16, allopatric distribution and specialization for serpentine soils. Shoot Ni-concentrations well above 1000 µg g-1 dry weight were confirmed for the Cretan population of O. baldaccii and found for the first time in two populations of O. stridii, which is therefore a new hyperaccumulating species of the Balkan Mediterranean flora. An updated key to the Greek Odontarrhena taxa is provided.