Isolates of Diplodia natalensis and Botryodiplodia theobromae were grown on synthetic media containing various concentrations of carbohydrate and nitrogen sources in different carbon:nitrogen ratios. Varying the ratio affected pigmentation, pycnidia shape and size, distribution of pycnidia, presence or absence and amount of stromata, presence or absence of hairs or setae on pycnidia, and number of pycnidiospores produced. Size and ornamentation of pycnidiospores were least affected. D. natalensis and B. theobromae are considered synonymous, since the results show that characters used previously for identification are significantly influenced by the growth media.