Molecular Insights into the Centaurea Calocephala Complex (Compositae) from the Balkans—Does Phylogeny Match Systematics?

Abstract

Groups of recent speciation are characterized by high levels of introgression and gene flow, which often confounds delimitation of species on a DNA basis. We analyzed nuclear DNA sequences (ETS spacer and the AGT1 gene) obtained from a large sample of the C. calocephala complex from the Balkan clade of Centaurea sect. Acrocentron (Compositae, Cardueae-Centaureinae) together with a wide representation of other species from the section. Our main goals were to verify the monophyly of the complex as currently defined and to examine the possible presence of introgression and gene flow. Within the complex, species are well-delimited from a morphological point of view and probably originated by allopatric speciation in the Balkan Peninsula. Our results confirm that the Balkan–Eurasian complex is a natural group, but the Centaurea calocephala complex shows a very complicated pattern and its phylogeny is not resolved. Our hypothesis suggests that altitudinal shifts in the transits from glacial to interglacial periods caused successive hybridization events, which are very evident from the DNA networks, between taxa not currently sympatric. As a result, confirmation of interspecific boundaries using molecular markers is extremely complicated.

African Mountain Thistles: Three New Genera in the Carduus-Cirsium Group

“…Such incongruences may result from several non-exclusive factors that promote unstable phylogenetic relationships, such as rapid radiations, ILS and hybridization [58][59][60]. Indeed, hybridization or introgression have been reported multiple times in the evolutionary history of the tribe Cardueae, e.g., [61].…”

Nomenclature and typification of plant names related to Centaurea aplolepa and C. leucophaea (Asteraceae) from Italy and France

“…Other authors, using more informative molecular approaches at finer geographic scales, were able to better clarify the taxonomy of critical species groups such as the C. cineraria L. group in the central Mediterranean ( Hilpold et al 2011 ), the C. calocephala Willd. group in the Balkans ( Novaković et al 2022 ), and the C. tenorei Guss. ex Lacaita group in southern Italy ( De Luca et al 2023 ).…”

Genotyping-by-sequencing provides new genetic and taxonomic insights in the critical group of Centaurea tenorei

“…Taxonomy and phylogeny of genus Centaurea L. have been intensely investigated in the last years, from both a morphological and molecular point of view (e.g., Font et al., 2002 ; Garcia-Jacas et al., 2006 ; Suarez-Santiago et al., 2007 ; Garcia-Jacas et al., 2009 ; Hilpold et al., 2011 ; Hilpold et al., 2014b ; López-Alvarado et al., 2014 ; Ranjbar and Negaresh, 2014 ; Bona, 2015 ; Arnelas et al., 2018 ; Arnelas et al., 2020 ; Del Guacchio et al., 2020a ; Novaković et al., 2022 ). Various of these contributions show that patterns of descent in this genus do not mirror the current taxonomy and indeed are more often associated to geographical proximity; this has been interpreted as the result of diffuse hybridization/introgression and gene flow between divergent populations, species and even sections in a context of overall low molecular variation or of Incomplete Lineage Sorting (ILS), complicated by convergence in diagnostic morphological traits ( Suarez-Santiago et al., 2007 ; Hilpold et al., 2014a ).…”

“…Various of these contributions show that patterns of descent in this genus do not mirror the current taxonomy and indeed are more often associated to geographical proximity; this has been interpreted as the result of diffuse hybridization/introgression and gene flow between divergent populations, species and even sections in a context of overall low molecular variation or of Incomplete Lineage Sorting (ILS), complicated by convergence in diagnostic morphological traits ( Suarez-Santiago et al., 2007 ; Hilpold et al., 2014a ). As a consequence, species sampled in multiple populations are “almost never monophyletic” ( Hilpold et al., 2014b , p. 205), incongruence in gene trees is rampant, and phylogeny does not necessarily correspond to systematics ( Hilpold et al., 2014b ; López-Alvarado et al., 2014 ; Novaković et al., 2022 ).…”

“…Moreover, they may be involved in the origin of new species ( Garcia-Jacas, 1998 ; Koutecký, 2007 ; Garcia-Jacas et al., 2009 ; Mráz et al., 2012 ; Merle et al., 2022 ), or even in the appearance of highly invasive hybrids ( Blair and Hufbauer, 2010 ). All these phenomena (i.e., hybridization, ILS, low molecular variation, convergence, intraspecific ploidy variation, polyploid origin of species) generate pervasive incongruence between phylogenetic hypotheses, and poorly supported trees ( Hilpold et al., 2014a ; López-Alvarado et al., 2014 ); this in turn greatly complicates taxa delimitation (e.g., Novaković et al., 2022 ) and phylogenetic inference (e.g., Hilpold et al., 2014b ).…”