Abstract— Conyza notobellidiastrum and C. rivularis are two South American species that recently were transferred to Podocoma, based mainly on corolla, style, and cypsela characters. Following evidence obtained from comparative morphological and
molecular studies developed in Podocoma, Podocominae, and Astereae in general, Conyza notobellidiastrum and C. rivularis were excluded from Podocoma. A new genus, Exostigma, is described to include these two species: Exostigma notobellidiastrum
and E. rivulare. Moreover, C. notobellidiastrum var. oblongifolia is placed in synonymy with. C. primulifolia, lectotypes are designated for the names Conyza notobellidiastrum and C. rivularis, and the appropriate new combinations are made.