Disentangling Crocus Series Verni and Its Polyploids

Abstract

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.

Phylogenomic investigation of safflower (Carthamus tinctorius) and related species using genotyping-by-sequencing (GBS)

“…Here we performed phylogenetic and population genomic analyses based on genome-wide distributed SNPs that were obtained through GBS to clarify the phylogenetic relationships of the relatives of C. tinctorius and to see if described ecotypes of safflower are genetically distinct. The GBS approach is known to have the potential for better-resolved relationships within and among closely related species in comparison to earlier fragment size analyses or sequence comparisons of single nuclear or chloroplast DNA regions [32][33][34][35][36] .…”

Crocus heuffelianus—A New Species for the Bulgarian Flora from Series Verni (Iridaceae)

“…There are controversies and uncertainties related to the systematics and phylogenetic relationships within taxonomic groups. One critical group is the Verni series, with mostly spring-flowering crocuses from central and southern Europe, some of which are important ornamentals [3]. So far, C. tommasinianus Herb is the only known Bulgarian flora from the series Verni.…”

“…Crocus vernus is a European alpine species, with a general distribution in the Pyrenees and Alps, east to Ukraine, and south to Sicily and Albania [2,6]. Recent phylogenetic analyses of polyploid lines from C. heuffelianus [3] testify to an allotetraploid origin resulting from the multiple reciprocal crosses between diploid genotypes of C. heuffelianus and C. vernus.…”

“…The phylogenetic relationships in the group are unclear. There are difficulties related to species differentiation, nomenclature, synonymy, and taxonomic affiliation [3,18]. A study of the populations of ser.…”

Advances in Plant Taxonomy and Systematics

“…The systematics of polyploid and/or apomictic species complexes was studied in European groups such as the Ranunculus auricomus complex (Ranunculaceae, Ranunculales, eudicots) [ 28 ], the Sorbus austriaca complex (Rosaceae, Rosales, eudicots) [ 29 ], Crocus ser. Verni (Iridaceae, Asparagales, monocots) [ 30 ], and Leucanthemum (Asteraceae, Asterales, eudicots) [ 31 ]. Integrated taxonomic approaches were followed for the characterization of the Asian palm genus Bentinckia (Arecaceae, Arecales, monocots) [ 32 ], for addressing infraspecific variability in the European Armeria arenaria (Plumbaginaceae, Caryophyllales, eudicots) [ 33 ], and for describing a new species endemic to Italy in Adonis sect.…”