Hybridization may endanger the rare North Apennine endemic Cirsium bertolonii

Abstract

We examined populations of North Apennine stenoendemics Cirsium bertolonii in the Apuan Alps and Tuscan-Emilian Apennines and found individuals morphologically shifted to co-occurring C. acaulon or C. erisithales. Hybrid status of these intermediates was confirmed by flow cytometry, morphometrics and amplified fragment length polymorphism (AFLP). We interpreted these hybrids taxonomically as Cirsium ×sagrense (C. acaulon × C. bertolonii) and C. ×abetonense (C. bertolonii × C. erisithales). Estimated genome size (2C) was 2244 ± 31 Mbp for C. ×sagrense and 2152 ± 99 Mbp for C. ×abetonense. Their genomic GC content was 38.95 ± 0.35% and 38.77 ± 0.26%, respectively. Diploid chromosome number 2n = 34 was counted for C. bertolonii, and the previously reported 2n = 12 needs to be considered erroneous. We found C. bertolonii to be a gynodioecious species (like many other Cirsium species) that is not reproductively isolated by ploidy level or chromosome number from co-occurring congeners. The relatively frequent occurrence of C. ×sagrense in Monte Sagro (locus classicus of C. bertolonii) and the prevalence of C. ×abetonense in Alpe Tre Potenze suggest that hybridization occurs repeatedly in C. bertolonii, as also confirmed by older herbarium specimens. C. ×abetonense produces ripe achenes and F2 hybrids or backcrosses, as some other Cirsium hybrids do. Genetic erosion/swamping via interspecific hybridization can therefore pose a risk to the genetic integrity of C. bertolonii, as it does for some other narrowly endemic high-mountain Cirsium species in Europe.

Intergeneric hybrid origin of the invasive tetraploid Cirsium vulgare

“…2007; Michálková et al . 2018, 2023), of all herbarium specimens of putative hybrids may potentially reveal that many of them are only defect/pauperized individuals of pure species (see Table S5C), where morphology‐based reassessment calls into question the existence of nearly half of the intergeneric Cirsium – Lophiolepis hybrids for which specimens were accessible. During our revision of Central European herbaria, we discovered that among specimens initially identified as hybrids, 9.9% were, in fact, pure species, and 5.3% were other hybrids.…”

“…Moreover, although intergeneric hybrids are also reported between Cirsium and Carduus (see Vukotinović 1877, p. 206;Guétrot 1925, p. 29;Fournier 1928Fournier , p. 277, 1940Fournier , p. 1001Fournier -1004Sennen 1931, p. 19), it was never used as an argument against the taxonomic relevance of these genera. Nevertheless, a comprehensive revision, ideally supported by molecular analyses (Segarra-Moragues et al 2007;Michálková et al 2018Michálková et al , 2023, of all herbarium specimens of putative hybrids may potentially reveal that many of them are only defect/pauperized individuals of pure species (see Table S5C), where morphology-based reassessment calls into question the existence of nearly half of the intergeneric Cirsium-Lophiolepis hybrids for which specimens were accessible. During our revision of Central European herbaria, we discovered that among specimens initially identified as hybrids, 9.9% were, in fact, pure species, and 5.3% were other hybrids.…”