A diploid drop in the tetraploid ocean: hybridization and long-term survival of a singular population of Centaurea weldeniana Rchb. (Asteraceae), a taxon new to Austria

A population of Centaurea weldeniana was discovered recently near Wien (Vienna). The species is reported from Austria for the first time. Determination is confirmed by morphometric analysis of Central European and additional Balkan material of the C. jacea agg. and karyological data. All sampled populations of C. weldeniana are diploid, while only tetraploids have been reported from Central Europe within the C. jacea agg. so far. Detailed morphometric analysis of the newly discovered C. weldeniana population revealed several hybrids with tetraploid C. jacea. The hybrids are tetraploid and originate from unreduced gametes of diploids. No triploids were found. Indeed, the incidence of hybridization is surprisingly low. The population was probably discovered already in 1886 (determined as C. bracteata) and was described as a new species C. argyrolepis in 1901, but these data were lost. However, this isolated diploid population has survived for at least 125?years, which provides a good example of the strength of inter-cytotype reproductive barriers in Centaurea sect. Jacea.