Luzula sect. Luzula is one of the taxonomically most intricate groups of angiosperms, where diversification is mostly driven by true polyploidy and agmatoploidy (fission of chromosomes) leading to three different karyotypes (whole chromosomes -AL, halfsized chromosomes -BL and quarter-sized chromosomes -CL). Morphologically, the taxa are often difficult to distinguish, and genome size data coupled with karyological investigations are currently the most reliable means for their identification. For the Balkan Peninsula, one of the botanically least studied areas of Europe, ten taxa from this section have been reported, but little is known about their distribution. We here estimated the nuclear DNA amount (genome size, GS) using interphase-peak DNA image cytometry and counted the chromosomes for 33 populations of five species of Luzula sect. Luzula mostly from mountainous areas of the Balkan Peninsula and the adjacent southeastern Alps. Five taxa have been confirmed, of which L. divulgatiformis is new for Croatia and L. exspectata for Macedonia and Serbia. The most common species in the Dinaric mountains appears to be diploid (2n = 12 AL) L. taurica, for which the GS (2C = 0.83 pg DNA, fitting well in the range of previously determined values of diploid taxa) has been determined for the first time. The GS and karyotypes of other taxa (L. campestris, L. divulgatiformis, L. exspectata, L. multiflora subsp. multiflora) correspond well to previously published values. An identification key for the Balkan taxa of Luzula sect. Luzula is also included.

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.Publisher's Note Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

Bačič T., Dolenc Koce J. and Jogan N. 2007. Luzula sect. Luzula (Juncaceae) in the South-Eastern Alps: morphology, determination and geographic distribution. Bot. Helv. 117: 75 -88.Within the genus Luzula, the type section (Luzula sect. Luzula) is particularly variable and taxonomically diverse. Eight taxa of Luzula sect. Luzula occur in the Alps. While these taxa have distinct caryotypes, their identification based on morphological traits has remained problematic, and their geographic distribution is insufficiently known. A morphometric study was performed on herbarium material from Slovenia and neighbouring regions to identify additional discriminative characters and to establish the distribution of taxa within the territory of Slovenia. We measured 52 plant traits on 233 herbarium sheets and analysed the data with multivariate statistical techniques. Results showed a clear differentiation between L. campestris and the seven other taxa, which were only discriminated by combinations of several quantitative characters. In general, ripe fruits are required for a reliable determination. Four of the eight taxa are widespread in Slovenia: L. campestris and L. divulgatiformis in the lowlands (mostly < 800 m), L. exspectata at higher altitude (> 900 m), and L. multiflora across a broad altitudinal range (200 -1900 m). Two taxa (L. divulgata and L. alpina) proved to be rare in Slovenia, and two taxa (L. sudetica and L. pallescens), previously reported for the area, were not confirmed. Distribution maps are presented for the six Slovenian taxa, and a new determination key is proposed for the eight Alpine taxa.

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