Diversification of Luzula sect. Luzula (Juncaceae) on the Balkan Peninsula – a cytogenetic approach

Abstract

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.

Diversification and distribution patterns of Luzula sect. Luzula (Juncaceae) in the Eastern Alps: a cytogenetic approach combined with extensive herbarium revisions

“…It comprises 59 species and numerous infraspecific taxa, which are very similar in habit and difficult to distinguish morphologically (Záveská Drábková 2013). The main differences are in minor quantitative traits, which are very variable (Kirschner 1993(Kirschner , 2002Bačič et al 2007bBačič et al , 2016. For a reliable identification of taxa, genome size (GS) data coupled with karyological investigations are ideal, but time consuming to obtain; furthermore, the latter rely on freshly collected seeds.…”

“…Diversification of Luzula has been strongly influenced by polyploidisation, which was an important driving force in the evolution of Angiosperms (Soltis et al 2009;Husband et al 2013;Weiss-Schneeweiss et al 2013) and is also one of the major factors affecting high mountain biodiversity in the Alps (Burnier et al 2009;Guggisberg et al 2009;Casazza et al 2012;Pachschwöll et al 2015). Contrary to true polyploidy, where GS at least initially increases linearly with the increased ploidy level, in the case of agmatoploidy (Malheiros and Gardé 1950;Löve et al 1957;Luceña and Guerra 1996) the increase in chromosome number is not correlated with an increase of GS; instead, the nuclear DNA amount is retained (Mello-Sampayo 1961;Bačič et al 2007a;Guerra 2016). Agmatoploidy is based on fission of holocentric (holokinetic) chromosomes; in contrast to the "normal type" of monocentric chromosomes, where spindle microtubules attach to a single kinetochore during mitosis or meiosis, in holocentric chromosomes they attach along the whole length through diffuse kinetochores (Bureš et al 2013).…”

“…As a result of agmatoploidy, chromosomes of three different sizes have been reported. The largest, full-size chromosomes are designated as AL-type, intermediate, half-size chromosomes as BL-type, and the smallest, quarter-size chromosomes as CL-type (Nordenskiöld 1951;Bačič et al 2007a;Bozek et al 2012). Alongside agmatoploidy, true polyploidy also played an important role in the diversification of Luzula sect.…”

“…Luzula (Malheiros and Gardé 1950;Nordenskiöld 1951Nordenskiöld , 1 3 1956Kirschner 1992a, b;Bačič et al 2007a;Bozek et al 2012). The most common karyotypes in the section are thus attributable to either true polyploidy (2n = 12 AL, diploid; 2n = 24 AL, tetraploid; 2n = 36 AL, hexaploid), complete agmatoploidy (2n = 24 BL, 2n = 48 CL) or mixed karyotypes, i.e., partial agmatoploidy (2n = 12 AL + 24 BL) (Nordenskiöld 1951(Nordenskiöld , 1956Kirschner 1992aKirschner , 2002Bačič et al 2007a;Bozek et al 2012;Záveská Drábková 2013;Bačič et al 2016). In a phylogenetic study of Luzula based on plastid trnL-F and internal transcribed spacer (ITS) sequences (Bozek et al 2012), relationships among the Alpine species and most other members of L. sect.…”

“…The distribution of species of L. sect. Luzula is insufficiently known due to frequent misidentifications (Bačič et al 2007b) and the recent description of two new species, rendering many previous records unreliable (Bačič et al 2007a). Before the two new species were discovered based on their peculiar karyotype, plants belonging to L. exspectata were mostly treated as L. alpina, L. multiflora and L. sudetica (particularly in Slovenia) or remained unidentified as L. multiflora agg., whereas those belonging to L. divulgatiformis were identified as L. campestris, L. multiflora and L. campestris agg.…”