No confirmation for previously suggested presence of diploid cytotypes of Sesleria (Poaceae) on the Balkan Peninsula

Abstract

The species-rich grass genus Sesleria is one of the most intricate genera of the European flora. Almost all species of the genus Sesleria are polyploid; only two species from the Alps, previously segregated as separate genera Psilathera and Sesleriella, are diploid. In addition, there is controversy about two diploid counts of S. comosa from the Bulgarian Rila and Pirin mountain ranges. These are the single reports of diploidy in Sesleria s. str., which would have significant impact on the future phylogenetic reconstruction of the genus’ evolutionary history. In order to confirm or reject these reports, we determined the relative DNA-content for 67 individuals of S. comosa from the two Bulgarian localities, from which diploid cytotypes have been reported. All analyzed individuals were clearly separated into two ploidy levels: DNA-tetraploids and DNA-octoploids. These results are in accordance with our previous comprehensive study on genome sizes in the genus, but are in stark contrast to the previous reports. Therefore, we suggest that the diploid counts rather refer to co-occurring, morphologically somewhat similar diploid Alopecurus gerardii, which has probably overgrown and outcompeted the slower growing and more susceptible S. comosa during cultivation before root tips were fixed for chromosome counting.