Integrative analysis of stem-reduction patterns in the inflorescences of Carlina acaulis subsp. caulescens from the Appennino Abruzzese Mountains (Central Italy)

Carlina species are well-known multi-use plants with edible, decorative, and officinal applications. In Italy, Carlina acaulis L., 1753 shows wide variability in stem length, ranging from acaulescent (non-stemmed) individuals to plants with a very prominent stem. This variability was often attributable to two subspecies presence, respectively: subsp. acaulis and subsp. caulescens (Lam.) Schübl. & G.Martens, 1834. According to recent references, subsp. acaulis is now to be considered restricted to north and central-northern Italy (including north Apennine), while subsp. caulescens can be found throughout the Italian peninsula, from north to south. However, specimens with strongly reduced stems can be observed even more at the south, like in our study area. In such cases, this variability is now to be considered as a simple intrasubspecific variability within subsp. caulescens . The apparent discrepancy between reduced and prominent stems within the same subspecies, although it could be a key morphological character for subspecies determination, is intriguing and warrants further investigation. How could this variability be influenced by genetic factors (i.e., internal subspecies variability, possible hybridization with similar taxa, or genetic remnants of subsp. acaulis ) or by environmental stressors/conditions? In our study, we examined the characteristics of C. a. subsp. caulescens alongside closely related taxa, looking for potential drivers of stem size by integrating botanical, environmental and ecological observations, morphological and chemical traits study, as well as genetic and soil microbiota analyses. These findings provide a multidisciplinary perspective on the factors shaping morphological and chemical diversity in Carlina taxa, offering new insights into their phenotype variation.