Out of the Balkans and Anatolia to the Western Alps? Surprising phylogenetic implications for two endemicAlyssum(Brassicaceae) species:A. cognensesp. nov. andA. rossetii

Abstract

The European Alps show a high degree of endemism associated mainly with the location of glacial refugia and environmental heterogeneity. Several Alpine endemics have evolved in the genus Alyssum. Here we study perennial Alyssum populations in the Western Alps, mainly distributed in the Aosta Valley region, which hosts high species diversity, although endemics are rare. We addressed the recently described stenoendemic A. rossetii and taxonomically uncertain populations usually attributed to A. montanum s.s. to clarify their phylogenetic position and morphological differentiation. The latter entity has been shown to be distinct from A. montanum s.s. and is described as a new species, Alyssum cognense, phylogenetically placed in the A. montanum–A. repens species complex. Both morphological and genetic patterns revealed that its closest relative occurs in the central Balkans. We present detailed ecological characteristics and morphological differentiation of A. cognense sp. nov. from its relatives and geographically closest species and speculate on its biogeographic origin. Genetic patterns (reduced diversity and nestedness) suggest long-distance dispersal from the central Balkan Peninsula. The second studied species, A. rossetii, is phylogenetically distant and belongs to the mainly Asian Alyssum section Gamosepalum lineage, which includes few representatives in southern and eastern Europe. The phylogenetically closest species of A. rossetii are Anatolian endemics, so this extreme disjunction remains puzzling. The present study illustrates the need for in-depth taxonomic and phylogenetic studies, even in well-explored Alpine regions, and also shows that the processes underlying the evolution of endemics can be complex and poorly understood.

An unexpected occurrence of Alyssum rossetii (Brassicaceae) in the Pyrenees, a new species for the Spanish flora

“…All data presented here, which include genome size values, morphological characters, and ITS sequences, are congruent and demonstrate that the Pyrenean plants growing between Pic de Qüenca and Rocablanca (684PQU) are conspecific with the population in the Valpelline valley (560FEU) in the Pennine Alps and should be classified as Alyssum rossetii . In concordance with previous phylogenetic inferences (Španiel & al. 2023a), A. rossetii is placed within the Gamosepalum lineage and is therefore phylogenetically distant from all other Alyssum species that occur both in the Pyrenees and in the Alps and adjacent regions.…”

“…Phylogenetic analyses and morphological evaluation included A. rossetii from the type locality in the Alps, and other perennial Alyssum species ( A. cacuminum , A. fastigiatum , A. montanum ) and annual species ( A. alyssoides , A. collinum , A. granatense and A. simplex ) previously reported from the Pyrenees and adjacent regions (Appendix 1). In addition, three species of the Gamosepalum lineage from Turkey, previously resolved as closest to A. rossetii (Španiel & al. 2023a), and Odontarrhena muralis (Waldst.…”

“…Ploidy levels of the other species were known from previous studies (Španiel & al. 2010, 2011a, 2018a, 2018b; Zozomová-Lihová & al.…”

“…The population is relatively small and until now no other localities have been recorded. Recent molecular studies revealed that it belongs to the Gamosepalum lineage (Španiel & al. 2023a, 2023b) and is phylogenetically placed closest to A. aurantiacum Boiss., A. misirdalianum Orcan & Binzet and A. praecox Boiss., all species known only from Turkey (Španiel & al.…”

“…The origin of such a large geographic disjunction (Alps versus Anatolia) is not clear. It might be a consequence of colonization events from Anatolia via the Balkans during glacial periods followed by range fragmentation and extinction in the intervening areas or a rare case of recent (Pleistocene) long-distance dispersal (Španiel & al. 2023a).…”