Acer opalus Miller 1768 because of its complex taxonomic status can be interpreted as a collective species which contains several species and subspecies depending on different interpretations. An important adventive occurrence from this collective species was found in a forest that belongs to the Tétényi plateau (Budapest, 11th district) in July of 2009. It is proved to be Acer opalus Mill. subsp. obtusatum (Waldst. et Kit. ex Wild.) Gams. The natural range of the subspecies covers the eastern side of the central Mediterranean Sea region and western Balkan Peninsula. It is a submediterranean-mediterranean, thermophile, shade-tolerant taxon but often appears together lightdemanding species too. In its native range it occurs in beech, pine, sessile oak forests and in different types of dry oak forests as admixed tree species. The subspecies was found in a turkey oak – sessile oak community in Hungary. Several old, seed growing individuals live on the spot which have had continuous seed production. Therefore from the old trees to the young seedlings different age categories are represented.