South America with half of all the known species represents most probably the primary diversity centre of the ascolocular lichen family Roccellaceae (Arthoniales). Nevertheless, neither a modem identification key nor a topical survey are available for the biologically, ecologically and phy- logenetically interesting taxa occurring on the mainland and (or) the adjacent islands. A computer- aided, dichotomous key has therefore been prepared, based as far as possible on easily detectable characters. All 51 species considered, belonging to 11 genera, are endemics. An appendix comprises nomenclatural, taxonomical and biogeographical additions, corrections and remarks. Among other items these embody diagnoses and descriptions of four new species: Roccella colonii Follm. sp. nov. (Galapagos Islands), R. humboldtiana Follm. sp. nov. (Northwestern Neotropics), R. transludica Follm. & B. Wern. sp. nov. (Galapagos Islands), Roccellina corrugata Follm. sp. nov. (North Chile). Dirina paradoxa f. sorediata Tehl. (North Pern) and Roccellina cerebriformis f. sorediata Tehl. (Cen tral Chile to Central Peru) are reduced to the synonymy of the corresponding typical species. In addi tion, the genus name Protoroccella Follm. is emended and validated with P. minima (Sant.) Follm. comb. nov. as generic type and P. follmannii (Sänch.-Pinto & M. Schulz) Follm. comb. nov. (both North Chile). At present, Camanchaca corallina Follm. & Peine, Protoroccella minima (Sant.) Follm. (both North Chile) and Roccella gayana Mont. (Central and South Chile) have to be regarded as seri ously endangered taxa, whereas R. babingtonii Mont., R. fragillima (Darb.) Follm. (both Central Chile) and R. nigerrima (Darb.) Follm. (Galapagos Islands) obviously became extinct within the re spective areas of distribution in recent times.