Contributo alla conoscenza delle praterie su substrati ultramafici dell’Alta Valtiberina (Toscana orientale, Italia).

Contribution to the knowledge of grasslands on ultramafìc substrata of the Upper Tiber Valley (Eastern Tuscany, Italy). - The Upper Tiber Valley is characterized by a wide diffusion of ultramafic substrata. The flora and vegetation of these substrata have been researched since the middle of the XX century. In recent years, phytosociological studies have allowed us to point out some peculiar vegetation types. In this paper the new association Festuco robustifoliae-Caricetum humilis is described. It consists of grassland phytocoenoses dominated by Carex humilis, Danthonia alpina and Festuca robustifolia, with Stipa etrusca, S. tirsa and Chrysopogon gryllus. Peculiar syntaxonomic, synchorologic and syndynamic aspects are shown.