New Zealand (NZ) spinach (Tetragonia tetragonoides) is an important leafy vegetable crop in Brazil and other countries. This plant is used as a substitute for common spinach because it is rustic and tolerant to tropical and subtropical environmental conditions. It is often affected by a leaf and stem spot disease, which increases in severity during the warm climatic periods. Cercospora tetragoniae has been reported as the cause of this disease, but this is based on an early description of a Cercospora-like species on this host in Argentina, first named Cercosporina tetragoniae but later recombined into Cercospora. In the present study, isolates of Cercospora-like fungi were obtained from NZ spinach and beetroot plants in Brazil, and a multigene molecular study including the act, cal, gapdh, his3, ITS, and tef1-α regions was carried out to identify the causative pathogen. Additionally, morphological and cross inoculation studies were conducted with isolates obtained from diseased plants. The pathogen was confirmed as Cercospora beticola, a common and harmful pathogen of beetroot (Beta vulgaris). Cross-inoculations of isolates obtained from NZ spinach and beetroot showed that the isolates are infective to both hosts. This increases knowledge of epidemiology and management of this important disease. Several attempts to re-collect samples from the type locality in Argentina failed. NZ spinach is no longer grown at La Plata (Argentina), the type locality of C. tetragoniae. Therefore, the task of re-collecting the pathogen is still pending, for epitype designation and for a full clarification of the taxonomic status of C. tetragoniae. The possibility of the pathogen being seed-transmitted has been assessed, and evidence obtained justifies further assessment of this aspect.