Alyssum rossetii, a stenoendemic madwort discovered on a mountain slope in the Valpelline valley (northern part of the Aosta Valley in the Pennine Alps), is described here as a new species. It is a perennial that is morphologically close to the Alyssum montanum-A. repens complex, with several hitherto neglected peculiar morphological characters. Here we present a full description of the new taxon, including information on its chromosome number, genome size and ecology, as well as a detailed morphological comparison of the new species with four related taxa occuring in the broader region, namely A. flexicaule, A. montanum, A. orophilum and A. rhodanense. Besides morphological differences, the new species also conspicuously differs from the other taxa in relative monoploid genome size. According to the IUCN Red List categories and criteria, it should be classified as Endangered.

The Mediterranean Basin is a significant hotspot of species diversity and endemism, with various distribution patterns and speciation mechanisms observed in its flora. High species diversity in the Mediterranean is also manifested in the monophyletic lineage of Alyssum annuals (Brassicaceae), but little is known about its origin. These species include both diploids and polyploids that grow mainly in open and disturbed sites across a wide elevational span and show contrasting distribution patterns, ranging from broadly distributed Eurasian species to narrow island endemics. Here, we investigated the evolution of European representatives of this lineage, and aimed to reconstruct their phylogeny, polyploid and genome size evolution using flow cytometric analyses, chloroplast and nuclear high- and low-copy DNA markers. The origin and early diversification of the studied Alyssum lineage could be dated back to the Late Miocene/Pliocene and were likely promoted by the onset of the Mediterranean climate, whereas most of the extant species originated during the Pleistocene. The Aegean region represents a significant diversity center, as it hosts 12 out of 16 recognized European species and comprises several (sub)endemics placed in distinct phylogenetic clades. Because several species, including the closest relatives, occur here sympatrically without apparent niche differences, we can reject simple allopatric speciation via vicariance as well as ecological speciation for most cases. Instead, we suggest scenarios of more complex speciation processes that involved repeated range shifts in response to sea-level changes and recurrent land connections and disconnections since the Pliocene. In addition, multiple polyploidization events significantly contributed to species diversity across the entire distribution range. All seven polyploids, representing both widespread species and endemics to the western or eastern Mediterranean, were inferred to be allopolyploids. Finally, the current distribution patterns have likely been affected also by the human factor (farming and grazing). This study illustrates the complexity of evolutionary and speciation processes in the Mediterranean flora.

A recent study of European annual taxa of Alyssum has revealed that A. simplex includes two cytotypes (diploid and tetraploid) which differ in genetic markers, evolutionary history, and monoploid relative genome size. In this paper we present a new taxonomic treatment of A. simplex in which we treat the two cytotypes as two separate species. We select and discuss suitable names for both taxa (diploid A. simplex and tetraploid A. collinum), examine their morphological differences and survey their geographic distribution. In addition, we compare both cytotypes with the morphologically similar and genetically related species A. strigosum and designate lectotypes and a neotype of several relevant names.

Odontarrhena tortuosa is a herbaceous species occurring in steppe and rocky habitats of Eurasia. The present study is focused on the cytogeography and morphological variation of the species’ populations growing in the Pannonian basin (Central Europe), which represents the westernmost part of its distribution area. Flow cytometric analyses have revealed the existence of tetraploid populations, which are reported here for the first time for Central Europe. We analysed the morphological variation of 329 individuals from Slovakia, Hungary and Serbia by multivariate morphometric methods to evaluate morphological differences between two cytotypes (diploids and tetraploids), between the subspecies (O. tortuosa subsp. tortuosa and O. tortuosa subsp. heterophylla) and between populations growing in three regions differing in the type of substrate (rocks, sand dunes and sandy and rocky screes). Although we have not found any clear morphological differences between the cytotypes, we have confirmed several previously reported morphological differences between the two subspecies, which occur in regions differing in the type of substrate. Flow cytometric data also indicate certain differences in monoploid genome size between all groups of populations under comparison. Populations from Serbia differ from other populations of O. tortuosa subsp. tortuosa in morphology and genome size, but due to a lack of data on the genetic variation of the species we suggest no change in taxonomy. For the identification of the two subspecies, we present an updated determination key.