Application of Indicator Species Analysis to communities with Stipa austroitalica Martinovsky and relevant syntaxonomic problems. According to the “Habitat” European Directive, Stipa austroitalica Martinovsky is a priority species. Its distributional range covers a large part of the south of Italy where the most representative populations occur in Apulia and Basilicata regions. Previous phytosociological studies which have regarded the Stipa austroitalica communities of southern Italy included these latter in Hippocrepido-Stipion austroitalicae (Scorzonero-Chrysopogonetalia, Festuco-Brometea), and, for a minor part, in Hyparrhenion hirtae (Hyparrhenietalia hirtae, Lygeo-Stipetea). In the present paper, new phytosociological data concerning some areas of great biogeographical importance such as Murge Plateau and Subappennino Dauno are presented. The new relevés were included in a larger data-set composed of all the Stipa austroitalica communities relevés published so far. The new matrix was further subjected to multivariate analysis procedures. Differently from the past, where the diagnostic species were chosen through traditional methods, in the present paper the Indicator Species Analysis (Dufrêne & Legendre, 1997) was applied in order to identify by “objective” criteria both community types and relative diagnostic species. The results have shown new groups of character species for the various community types identified. Furthermore a critical analysis of the syntaxonomical relationship between Scorzonero-Chrysopogonetalia and Hyparrhenietalia hirtae orders was discussed. In particular, the phytosociological comparison amongst the various Stipa austroitalica communities described so far, suggests the possibility to reconsider the syntaxonomical hypothesis proposed by Horvatić (1975) who divided Scorzonero-Chrysopogonetalia into two new orders where one of these, Koelerietalia splendentis, included the more termophilous Mediterranean types.