Comparative molecular cytogenetic analyses introduced for Taxa of the genus Helictotrichon and related genera from Aveneae (Agrostis, Ammophila, Amphibromus, Arrhenatherum, Avena, Deschampsia, Holcus, Koeleria, Lagurus, Pseudarrhenatherum and Trisetum), some genera of the phyla Poeae (Cynosurus, Festuca), Seslerieae (Sesleria) und Triticeae (Elymus); as well as the subfamilies Arundinoideae (Arundo, Danthonia) and Stipoideae (Stipa) from the grass family Poaceae. Karyotype analyses contain the traditional "karyotyping" for chromosome number, -size and -morphology; fluorochrome banding; silver impregnation; and physical mapping of 5S and 45S rDNA as well as three satellite DNA’s (CON1, CON2, COM2) using in situ hybridisation. Ideograms were constructed using karyotype parameters. In the molecular aspects of chromosomal differentiation hitherto unknown regularities in the occurrence and distribution of ribosomal DNA’s, satellite DNA and heterochromatin are discussed. The possible parentage of polyploids is reconstructed on the basis of 17 identified basic chromosome sets. The majority of polyploid taxa are created by means of alloploidy. The multitude of combinations of basic chromosome sets is clearly related to the high morphological anatomical "plasticity" of the taxa and serves as a good example of the "reticulate evolution" of polyploid complexes. Acknowledging chromosomal characteristics, the four subgenera of Helictotrichon are clearly monophyletic. However, the genus Helictotrichon, in the traditional sense, is apparently a paraphyletic, if not a polyphyletic taxon. The karyotype evolution is interpreted in light of existing molecular phylogenies. Chromosomal apomorphies and plesiomorphies are introduced. The karyotype differentiation is partly related to ecological and chorological data. Finally, the relevance of chromosomal data to "greater systematic" questions within the family is clarified. In connection with this, it is demonstrated that the genus Danthoniastrum, as a primitive Aveneae in the subfamily Pooideae, was incorrectly classified, and actually belongs to the subfamily Stipoideae.