In the spring and summer of 2010 a number of new localities of the southeastern-Alpine endemic Leontodon hispidus subsp. brumatii were found on temporarily flooded riparian rocks in the gorge of the Sava River between the village of Sava and Zidani Most (central Slovenia). The species has so far been known only in northeastern Italy and western Slovenia (the So a valley). In order to obtain more specific information its sites were studied phytosociologically and the communities in which it grows in the Sava and the So a valleys compared. Two new associations were described on the basis of these comparisons: Triseto argentei-Leontodontetum brumatii ass. nov. and Leontodonti brumatii-Seslerietum calcariae ass. nov. As this endemic taxon and its endemic communities are a characteristic of riparian flora and vegetation of some Slovenian mountain rivers and as its localities in the Sava valley are explicitly disjunct and the southeastern-most in the entire known distribution area, they deserve to be studied and protected.