In Flora Uruguaya, José Arechavaleta described two Uruguayan species of Myosotis L. (Boraginaceae) that I. M. Johnston later placed within Antiphytum DC. ex Meisn. Johnston considered M. uruguayensis Arechav. to be a doubtful species that was probably in Antiphytum, apparently nearest to A. cruciatum (Cham.) DC., whereas he treated M. berroi Arechav. as a synonym of A. stoechadifolium (Cham.) DC. We studied the type specimens and protologues of these two names in Myosotis. We conclude that M. berroi belongs to Antiphytum but is not conspecific with A. stoechadifolium based on eremocarp features, such as pericarp ornamentation and size, together with shorter leaves. We provide an updated circumscription and distribution, publish the new combination A. berroi (Arechav.) N. Mend. & Flores Olv., and clarify the type. A taxonomic key for the South American species of Antiphytum is provided. Myosotis uruguayensis does not belong to Antiphytum due to its shallowly divided calyx entirely covering the immature eremocarps; it retains its uncertain taxonomic status due to the scanty and immature original material and inadequate protologue.