Spring crocuses, the eleven species within Crocus series Verni (Iridaceae), consist of di- and tetraploid cytotypes. Among them is a group of polyploids from southeastern Europe with yet-unclear taxonomic affiliation. Crocuses are generally characterized by complex dysploid chromosome number changes, preventing a clear correlation between these numbers and ploidy levels. To reconstruct the evolutionary history of series Verni and particularly its polyploid lineages associated with C. heuffelianus, we used an approach combining phylogenetic analyses of two chloroplast regions, 14 nuclear single-copy genes plus rDNA spacers, genome-wide genotyping-by-sequencing (GBS) data, and morphometry with ploidy estimations through genome size measurements, analysis of genomic heterozygosity frequencies and co-ancestry, and chromosome number counts. Chromosome numbers varied widely in diploids with 2n = 8, 10, 12, 14, 16, and 28 and tetraploid species or cytotypes with 2n = 16, 18, 20, and 22 chromosomes. Crocus longiflorus, the diploid with the highest chromosome number, possesses the smallest genome (2C = 3.21 pg), while the largest diploid genomes are in a range of 2C = 7–8 pg. Tetraploid genomes have 2C values between 10.88 pg and 12.84 pg. Heterozygosity distribution correlates strongly with genome size classes and allows discernment of di- and tetraploid cytotypes. Our phylogenetic analyses showed that polyploids in the C. heuffelianus group are allotetraploids derived from multiple and partly reciprocal crosses involving different genotypes of diploid C. heuffelianus (2n = 10) and C. vernus (2n = 8). Dysploid karyotype changes after polyploidization resulted in the tetraploid cytotypes with 20 and 22 chromosomes. The multi-data approach we used here for series Verni, combining evidence from nuclear and chloroplast phylogenies, genome sizes, chromosome numbers, and genomic heterozygosity for ploidy estimations, provides a way to disentangle the evolution of plant taxa with complex karyotype changes that can be used for the analysis of other groups within Crocus and beyond. Comparing these results with morphometric analysis results in characters that can discern the different taxa currently subsumed under C. heuffelianus.

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Crocus cf. heuffelianus Herb. belongs to the series Verni Mathew and presents one of the most complex and critical taxa within the whole genus Crocus L. Depending on different authors, C. cf. heuffelianus is sometimes split into different taxa (e.g., C. scepusiensis (Rehmer & Wol.) Borbás ex Kulcz., C. vittatus Schloss. & Vuk., nom. illeg.). In order to disentangle the complicated taxonomical status of this species and to determine the degree of its morphoanatomical variability in the different environmental conditions, a comparative investigation of plant morphology and leaf anatomy of seven populations from the Balkan Peninsula was carried out. Morphometric analysis included meristic, quantitative, and qualitative parameters. To examine the leaf anatomy, fresh cross sections were made by manual microtome and stained with safranin and alcian blue. Statistical analyses, such as principal component analysis and canonical discriminant analysis revealed significant differences between populations, indicating the presence of distinct groups correlating with their geographical distribution. The largest contribution to the differentiation of analyzed populations is made by the characters that are related to corms, perigone segments, leaves, and anthers, followed by the general outlook of cross sections, palisade and spongy parenchyma, abaxial epidermal cells, and vascular bundle features. These findings confirm that from the morphoanatomical point of view Balkanian C. cf. heuffelianus presents an aggregate of species.

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