Rhotic representation: problems and proposals
M. Stanley Whitley · Journal of the International Phonetic Association · 2003
Starting with an r that was already ambiguous, the IPA added new symbols and diacritics without arriving at a comprehensive treatment of rhotics. The results have been ad hoc solutions and potential confusion for languages such as Spanish, in which these need to be distinguished. A few modifications of the IPA diacritic system would suffice in order to capture the different types.