Disentangling the taxonomic structure of the Allium paniculatum species complex in central and eastern Europe using molecular, cytogenetic and morphological tools

Abstract

Allium section Codonoprasum includes a group of evolutionarily young taxa with unclear taxonomic boundaries, evolutionary relationships and complex synonymy. The most complicated taxon in this section is A. paniculatum, which until recently was considered to be the most widespread and morphologically most variable species, with a distribution extending from the Mediterranean area to central Europe and the Pontic region. A recent taxonomic study has shown that true A. paniculatum is a morphologically and genetically distinct species occurring in southern Ukraine and southern Russia. The clarification of its taxonomic identity questioned the taxonomic identity of populations referred to as A. paniculatum in other parts of Europe, including populations in central (Slovakia, Hungary, northeast Serbia) and the western part of eastern Europe (Romania, Ukraine), from where four other species of this complex (i.e. A. fuscum, A. fussii, A. marginatum and A. podolicum) were described and later frequently merged as synonyms with A. paniculatum. Here, the diversification within this complex in the abovementioned region is explored, using various biosystematic methods (morphometry, leaf anatomy and epidermal micromorphometry, karyology, estimation of genome size and GC content using flow cytometry, and molecular fingerprinting using Amplified Fragment Length Polymorphisms). By this means the existence of three well-separated population groups were revealed in the material studied, taxonomically corresponding to A. fuscum, A. marginatum and the group A. paniculatum + A. podolicum. The genetic patterns indicate that populations of at least some of these taxa might have survived in their current ranges or in neighbouring areas during the last glacial and the early Holocene. Allium fuscum is a species that inhabits shaded rocky outcrops in the wide neighbourhood of the Iron Gate area (south-western Romania, north-western Bulgaria and northeast Serbia). Allium marginatum is a species closely related to A. fuscum, inhabiting dry grasslands and dry oak forests in the Pannonian and Transylvanian Basins. Two eastern-European taxa, A. podolicum and A. paniculatum,which are very similar inmorphology, genome size and genetic markers, are considered to be conspecific and named A. paniculatum. This species inhabits zonal steppe and forest steppe regions in eastern Europe from western Ukraine to southern Russia. In addition, a taxonomic and nomenclatural treatment, as well as a key for identifying the recognized species of the A. paniculatum complex in the region studied, are presented.