Santolina is a plant genus of dwarf aromatic shrubs that includes about 26 species native to the western Mediterranean Basin. In Corsica and Sardinia, two of the main islands of the Mediterranean, Santolina corsica (tetraploid) and S. insularis (hexaploid) are reported. Along with the cultivated pentaploid S. chamaecyparissus, these species form a group of taxa that is hard to distinguish only by morphology. Molecular (using ITS, trnH-psbA, trnL-trnF, trnQ-rps16, rps15-ycf1, psbM-trnD, and trnS-trnG), cypsela morpho-colorimetric, morphometric, and niche similarity analyses were conducted to investigate the diversity of plants belonging to this species group. Our results confute the current taxonomic hypothesis and suggest considering S. corsica and S. insularis as a single species. Moreover, molecular and morphometric results highlight the strong affinity between S. chamaecyparissus and the Santolina populations endemic to Corsica and Sardinia. Finally, the populations from south-western Sardinia, due to their high differentiation in the studied plastid markers and the different climatic niche with respect to all the other populations, could be considered as an evolutionary significant unit.

Three subspecies of Armeria arenaria are reported from Italy, two of which are considered endemic to the Apennines. The taxonomic value of these two taxa (A. arenaria subsp. marginata and A. arenaria subsp. apennina) is unclear. Moreover, the relationships between A. arenaria subsp. praecox and Northern Italian populations—currently ascribed to A. arenaria subsp. arenaria—have never been addressed. Accordingly, we used an integrated taxonomic approach, including morphometry, seed morpho–colorimetry, karyology, molecular systematics (psbA–trnH, trnQ–rps16, trnF–trnL, trnL–rpl32, and ITS region), and comparative niche analysis. According to our results, French–Northern Italian populations are clearly distinct from Apennine populations. In the first group, there is evidence which allows the recognition of A. arenaria s.str. (not occurring in Italy) and A. arenaria subsp. praecox. In the second group, the two putative taxa endemic to the Northern Apennines cannot be separated, so a single subspecies is here recognized: A. arenaria subsp. marginata.

The Santolina chamaecyparissus complex includes 13 species of dwarf aromatic evergreen shrubs from the western Mediterranean Basin. Five native species occurring in Italy are currently accepted. Four of them are endemic to relatively restricted areas in the peninsula, whereas S. corsica Jord. & Fourr. is endemic to Corsica and Sardinia. The taxonomic treatments of Italian S antolina have been changing significantly in the past, probably due to the misinterpretation of naturalised populations of S. chamaecyparissus , a widely cultivated pentaploid species, which occasionally escapes from cultivation through agamospermy or vegetative propagation. In this study, we carried out the first quantitative morphometric and comparative niche analyses concerning the four species endemic to continental Italy ( S. etrusca , S. ligustica , S. neapolitana , and S. pinnata ). Morphometric analyses (PCoA, Random Forest, and univariate analyses) show that these species can be easily distinguished by combinations of character states, whereas niche analyses (Schoener’s D and similarity test) suggest that they occur in distinct climatic conditions. Based on our results, we fully confirm the taxonomic distinctiveness of these species. An updated identification key, including all Santolina species occurring in Italy, is presented.

Many species exhibit intraspecific ecological variation, and to not consider this ecological differentiation can confound predictions made with species distribution models (SDMs). This problem may be particularly relevant for species where there are few populations with potential local adaptations. To increase the performance of niche models and provide more solid basis for conservation plans, it is recommended to apply a subdivision criterion with biological significance. In this study, we examined twelve species with disjunct populations and created models of both the entire species and each group of populations. In addition, we considered as an “aggregate model” for the species the area predicted to be suitable by at least one of each group of populations. In general, the highest range of contractions were identified by the species model. The species model forecasted a similar trend as the aggregate model in the majority of species, but in four cases they predicted opposite trends. In summary, our results suggest that the inclusion of intraspecific variability does not significantly improve the overall accuracy of SDMs based on all species occurrences, but may lead to substantially different conclusions about future range changes. Furthermore, they suggest that intraspecific variability alone may provide a buffer against environmental change, even if the niche is conserved among different intraspecific groups. Consideration of intraspecific differences may ultimately allow us to highlight potential resilience units that can act as potential buffers against the adverse effects of climate change, and to develop targeted conservation strategies accordingly.