Polyploidisation—and, additionally, agmatoploidy (concerted fission of chromosomes) in some plant groups—have significantly contributed to the diversification of alpine plant species. Both processes have driven the diversification of Luzula sect. Luzula , leading to a number of different karyotypes, rendering it one of the most intricate plant groups in the Alps. For the Eastern Alps eight species with six karyotypes were reported, but their distribution is insufficiently known. A herbarium revision of 1044 specimens revealed that L. alpina , L. campestris , L. exspectata , L. multiflora and L. sudetica are widespread across the Eastern Alps; L. exspectata is thus new for the Northern Alps and new for Germany, France and possibly Croatia. Luzula divulgata is distributed in the easternmost Alps and adjacent areas, with only a few indications for the western Eastern Alps. Luzula divulgatiformis is new for the Alps where it was recorded in the Southern Alps and southerly adjacent areas. Luzula campestris , L. divulgata and L. divulgatiformis are distributed from lowlands to the montane belt, L. alpina, L. exspectata and L. sudetica are high-elevation species and L. multiflora occurs from lowlands to the alpine belt. Additionally, we estimated genome size (GS) and karyotypes for 20 populations and revealed four karyotypes corresponding to three ploidy levels. The GS of diploid L. exspectata and L. sudetica was 0.83 pg DNA, tetraploid L. alpina had a double (1.63 pg) and hexaploid L. multiflora a triple (2.48 pg) GS. Our study underlines the importance of large-scale herbarium revisions of intricate taxa, combined with cytological methods, even in well-studied mountain areas such as the Alps and poses new hypotheses regarding the evolution of this polyploid–agmatoploid group.