Genista lydia Boiss. is an endemic Balkan-Anatolian species which forms rare communities in the territory of south Bulgaria and northeast Greece. They are spread exclusively on acidic, siliceous substrates. This study presents new data on their distribution, floristic and ecological structure and phytosociological affinities. The research is based on 156 phytosociological relevés. Unweighted pair–group method with arithmetic averages (UPGMA) was employed and a detrended correspondence analysis (DCA) was performed prior to the syntaxonomical decision. Three new associations and the new alliance Genistion lydiae have been described and classified within the order Lavandulo stoechadis-Hypericetalia olympici Mucina in Mucina et al. 2016 of the class Cisto-Lavanduletea stoechadis Br.-Bl. in Br.-Bl. et al. 1940. The study has also emphazised the potential threats concerning a decline of the habitat area and proposed some conservation measures.