Does chromosome number count? Mapping karyological knowledge on Italian flora in a phylogenetic framework

Abstract

Italian vascular flora is highly representative of the Euro-Mediterranean area, because the region includes high mountain territories, temperate areas, and regions dominated by the Mediterranean climate. Chromosome number information about the Italian flora stored in the online database Chrobase.it includes 6,756 records, referable to 3,539 cytotypes and 2,785 accepted species and subspecies (approx. 35% of the national flora). Appropriate queries to Chrobase.it enabled us to map chromosome numbers, at order rank, in a robust phylogenetic framework, derived from APGIII and other recent phylogenetic studies on vascular plants. Similar work was conducted for selected families and genera. Chromosome number data were available for 41 out of 80 vascular plant orders (51%) currently recognized world-wide and 107 out of 428 families (25%), represented by 661 genera (4.5%). The large number of records enabled us to compute the mean chromosome number for each taxon, and to highlight significant differences among all orders and among subsets of families and genera. For each taxon, we analysed the variability in chromosome number by use of common statistical methods, and computed the frequency of chromosome numbers, the coefficient of variation of chromosome number (CVCN), the frequency of B-chromosomes (fB), and that of odd chromosome numbers (fOCN). The phylogenetic relevance of our results is discussed and the usefulness of basic karyological data, often neglected in current phylogenetic studies, is stressed.