ABSTRACT: Epiphytic lichen diversity in Buenos Aires City is documented. A list of 50 species is presented. Haematomma subinnatum, Ramalina celastri, Teloschistes chrysophthalmus and Xanthoria fallax, registered during an earlier survey (1984), probably no longer exist in the city. 44% of the species were found only in squares or parks. Scoliciosporum chlorococcum is a new record for South America. Pyxine petricola, an unnamed species of Caloplaca with blackish apothecia (close to Caloplaca floridana), and an unnamed species of Endocarpon are new records for the Pampa region. A key to species is provided including species present both in the City and its surroundings. Thus, the present work is also applicable to a much more extensive urban area, "Gran Buenos Aires," providing a baseline for biomonitoring air pollution also in that region. As most species exhibited very low frequency and coverage, the key was especially designed to reduce as far as possible the need of collecting samples for examination in the laboratory. Comments on the most problematic taxa are included.

KEYWORDS: biodiversity, conservation, air pollution, key to species

NOMENCLATURAL NOVELTIES:
None.