Ecological patterns of morphological variation in Italian populations of Romulea bulbocodium (Iridaceae)

• Morphology of Romulea bulbocodium varied primarily across geographical range.
• R. bulbocodium phenotypes were influenced by habitat and soil chemistry.
• Some morphological characters varied in size with aridity and nutrient availability.
• Large morphological variations between inland magmatic and coastal calcareous sites.
• Two distinct ecotypes were identified in relation to habitat.

Romulea bulbocodium is a steno-Mediterranean species found in widely diverse habitats; it shows considerable morphological variations among different populations. The present study used morphological and numerical analyzes to investigate whether and how different habitats affect Italian populations of R. bulbocodium to generate ecological patterns of morphological variation. Individuals from 21 Italian populations in three geo-lithology based habitat types (coastal habitats on calcareous sediments and inland habitats on limestone or magmatic rocks) were sampled in three randomly chosen plots along transects. Morphological, soil chemistry and geographical parameters were measured. The results indicate that morphological variation in Italian populations of R. bulbocodium is associated primarily with geographical variables, reflecting climatic and edaphic factors. Sicilian individuals showed strong floral distinctness compared to individuals from other regions, underlining that local phenotypic differentiation is associated with geographic isolation. Furthermore, plants growing in magmatic habitats versus coastal habitats showed the largest morphological distinctness indicating that phenotypes are also influenced by soil chemistry and habitats. These morphological differences are linked to ecological factors such moisture and mineral content of soils. Flower characters that significantly distinguish Italian populations in different habitats has been used by other authors as diagnostic tools to differentiate species of the genus Romulea and we can suppose that they are constrained genetically. However, our results do not support the recognition of infraspecific taxa in R. bulbocodium but instead sustain the identification of two different ecotypes growing in calcareous coastal and inland magmatic habitats, respectively.