• Armeria
• biosystematics
• central Mediterranean
• integrative taxonomy
• nomenclature
• phylogeny
• Plumbaginaceae
• probabilistic modeling
• species delimitation
• supervised modelling

The present doctoral thesis is the result of a three-year PhD research project conducted at the University of Pisa that focuses on the challenging taxonomy and complex systematics of the genus Armeria Willd. (Plumbaginaceae) in the central Mediterranean, which includes 27 taxa, many of which are endemic to this area. The thesis begins by addressing the longstanding issue of species definition, exploring the historical and philosophical debates surrounding the question “What is a species?” and the lag between species circumscription methods and conceptual model behind the species. Next, I focus on the complexities of the genus Armeria, reviewing most of the existing bibliography. After, in three chapters, I apply an integrative taxonomic approach combined with a thorough nomenclatural study to clarify species boundaries and names, resolving taxonomic uncertainties within Armeria following an anticlockwise taxonomic-geographical structure. In the first chapter, I studied the taxonomy and systematics of the Armeria arenaria complex, applying morphometric analyses. This complex, recorded from the central Mediterranean to northern Italy and France, originally included four subspecies native to the central Mediterranean, now reduced to three with A. arenaria subsp. arenaria excluded from the flora of Italy. Secondly, I focused on the highly biodiverse Sardinian-Corsican block, which was thought to contain 10 endemic taxa. However, some of these were revealed to be altitudinal ecotypes and were synonymized, leading to the recognition of five taxa endemic to the region. Thirdly, I studied the variability of Armeria taxa across the Italian peninsula and Sicily, also considering the Balkan species A. canescens (Host) Ebel, which had long been thought to be native to the Apennines as well. The results confirm most of the species, with three relevant taxonomic changes: A. gracilis Ten. subsp. majellensis (Boiss.) Arrigoni is synonymized with A. gracilis Ten., A. canescens is definitely excluded from the Italian flora and the Pollino populations are recognized as a distinct species under the name A. pollinensis (N.Terracc.) Tiburtini & Peruzzi. I then present a revised taxonomic scheme for Armeria taxa endemic to the central Mediterranean, by providing a set of updated identification keys to facilitate other scholars or amateur botanist in the identification of the 20 accepted Armeria taxa. Throughout the chapters of this thesis, the reader will notice a marked shift in the methods used for species circumscription, driven by the recognition of a more probabilistic approach behind species delimitation. To address this issue, I developed and applied a probabilistic framework utilizing Gaussian Mixture Models (GMMs) for species delimitation based on morphological data. Lastly, I summarize the findings and discuss future perspectives on this and other topics.