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We describe four new species, Asterothyrium bisporum Ferraro & Lücking (Argentina); Asterothyrium rostratum Ferraro & Lücking, A. subargenteum Ferraro & Lücking and A. segmentatum Ferraro & Lücking (Paraguay). One new combination is made; Asterothyrium pallidum (Henssen & Lücking) Ferraro & Lücking comb. nov. based on A. anomalum var. pallidum Henssen & Lücking. We include a key and descriptions for the 14 species known from the region, some being first records.