Parallel bursts of recent and rapid radiation in the Mediterranean and Eritreo‐Arabian biodiversity hotspots as revealed byGlobulariaandCampylanthus(Plantaginaceae)

Abstract

Aim Molecular phylogenetic inferences have been important to test hypotheses of the temporal and geographical origin of plant lineages from the Mediterranean region (MR) and their rates of diversification. However, comparisons are still rare between well‐sampled and closely related clades from within and outside the MR. Here, we compare the biogeographical histories and diversification rates between two main genera of woody perennial Plantaginaceae with highest species diversities in the MR (Globularia) and the Eritreo‐Arabian region (EAR; Campylanthus). Location Mediterranean Basin and adjacent regions; Eritreo‐Arabian region. Methods We estimated a time‐calibrated phylogeny of the Globularia+Poskea–Campylanthus clade based on combined nuclear (ITS) and chloroplast DNA sequences for ancestral area reconstructions and within‐ and among‐clade diversification rate analyses. Results The presently disjunct ranges between Globularia and Campylanthus most likely reflect dispersal/migration from the EAR into the MR between the mid‐early Miocene (c. 9.6 Ma) and the late Pliocene (c. 3.3 Ma). The subsequent diversification of Globularia coincides with that of Campylanthus (c. 3.5 Ma), with similar rates of constant lineage accumulation in both genera. While the Macaronesian Globularia species are recent (Late Pleistocene) colonists, most likely from the MR, neither late Plio‐/Pleistocene vicariance nor dispersal‐mediated range evolution can be refuted for Macaronesian versus EAR Campylanthus. Main conclusions The coupling between low‐ and high‐latitude climate shifts likely triggered the simultaneous diversification at comparable rates of Campylanthus and Globularia in, respectively, the EAR and MR at the end of the Pliocene. In the extensive and ecogeographically complex MR, Globularia experienced increased diversification rates likely triggered by glacial cycles and resulting in adaptive species formation. In contrast, increased diversification rates in Campylanthus likely were triggered by aridity cycles and resulted in geographical speciation.

Explaining Intricate Morphometric Variability with Environmental Predictors: The Case of Globularia cordifolia Species Complex

“…Evidence from recent molecular data support the hypothesis that G. section Empetron is one of the latest branching lineages in the evolution of Globularia, and that G. meridionalis, G. cordifolia, and G. neapolitana are close to G. repens [1,5]. According to Milletti [6], such large variability could be explained by the wide area of occurrence of the species and their habitat fragmentation, noting a large polymorphism and quoting Willkomm [32] for the explanation, "Hic speciei typus per innumeras formas intermedias transit in varietatem" (English: "This type of species passes from variety to variety through countless intermediate forms").…”

“…The number of species belonging to this genus and their taxonomic status have been interpreted in several ways by the authors who have studied these plants over the years. Currently, 27 taxa are included in this genus [5], of which many are narrow endemics [1, 6,7]. Recent molecular studies have demonstrated that Globularia, which was traditionally included in a separate family (Globulariaceae) along with Poskea Vatke, actually belongs to Plantaginaceae [8].…”

“…Accordingly, representatives of the genus are widespread in most of Europe. However, the highest concentration of taxa is found in Central and Southern Europe, Anatolia, Northern Africa, and Macaronesia [1,5]. Disjunct populations are also found in the Atlantic and Swedish islands and around the Volga [5].…”

“…However, the highest concentration of taxa is found in Central and Southern Europe, Anatolia, Northern Africa, and Macaronesia [1,5]. Disjunct populations are also found in the Atlantic and Swedish islands and around the Volga [5]. Most species are adapted to dry and open habitats, often on calcareous soils, in meadows or on bare rocks [6].…”

“…According to Milletti [6], such large variability could be explained by the wide area of occurrence of the species and their habitat fragmentation, noting a large polymorphism and quoting Willkomm [32] for the explanation, "Hic speciei typus per innumeras formas intermedias transit in varietatem" (English: "This type of species passes from variety to variety through countless intermediate forms"). Admittedly, mechanisms of speciation are still poorly understood in Globularia, and fine-scale distributional, population genetic, morphological, and reproductive data are needed to further clarify the evolutionary history of these plants [5].…”