Life cycle versus systematic placement: phylogenetic and cytogenetic studies in annual Artemisia (Asteraceae, Anthemideae)

Abstract

Artemisia L. comprises ca. 20 annual species out of ca. 500, which are distributed mainly across the Old World grades, accounting for multiple independent acquisitions of annual habit throughout the evolutionary history of the genus. This makes Artemisia an interesting subject for the study of plant life cycle evolution in a phylogenetic context and its consequences at genomic level. The main aim of this phylogenetic analysis was to circumscribe 17 of the annual representatives within the major lineages of Artemisia. Genome size has been assessed and ancestral values reconstructed on the tree. Fluorescent in situ hybridisation (FISH) has also been performed to characterise the physical distribution of ribosomal DNA loci. Our results show that annual Artemisia have been especially misassigned at subgeneric level and confirm that they are phylogenetically restricted to basal grades, while absent from the derived ones. Annuals display great diversity of genomic traits; however, although most of them show genome downsizing with respect to their most recent common ancestors, no apparent correlation exists between this trait, the number of rDNA sites, and the phylogenetic placement. Nonetheless, such diversity suggests that higher rates of genome restructuring may have been key in governing genome evolution in annual species.